This document presents a multiwavelength analysis of the merging galaxy cluster MACS J0416.1-2403 using observations from Chandra, JVLA, GMRT, and Hubble Space Telescope. The cluster consists of two main subclusters, NE and SW, separated by about 250 kpc. Chandra observations reveal the NE subcluster has a compact core and X-ray cavity, but is not a cool core. A density discontinuity is detected about 450 kpc southwest of the SW subcluster, likely caused by an interaction with a less massive structure detected in lensing maps. For both subclusters, the dark matter and gas components are well-aligned, suggesting MACS J0416.1-2403
The discovery of_lensed_radio_and_x-ray_sources_behind_the_frontier_fields_cl...Sérgio Sacani
We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster
MACSJ0717.5+3745. MACSJ0717.5+3745 offers the largest contiguous magnified area of any known cluster,
making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0–6.5 GHz
JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the
HST imaging. Within this sample, we find sevenlensed sources with amplification factors larger than two. None of
these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are
likely star-forming galaxies with star-formation rates (SFRs) of 10–50 M: yr−1 located at 1 1 z 1 2. Two of the
lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic
nuclei, given their 2–10 keV X-ray luminosities of ∼1043–44 erg s−1. From the derived radio luminosity function, we
find evidence for an increase in the number density of radio sources at 0.6 z 2.0, compared to a z 0.3 sample.
Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with
SFRs as low as ∼10Me yr−1, at the peak of cosmic star formation history.
Imaging the dust_sublimation_front_of_a_circumbinary_diskSérgio Sacani
Aims. We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust.
Methods. A very rich interferometric data set in six spectral channels was acquired of IRAS 08544-4431 with the new RAPID camera
on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the H-band was reconstructed
by combining the data of all spectral channels using the SPARCO method.
Results. We spatially separate all the building blocks of the IRAS 08544-4431 system in our milliarcsecond-resolution image. Our
dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an
unexpected flux signal of 4% from the secondary star. The energy output from this companion indicates the presence of a compact
circum-companion accretion disk, which is likely the origin of the fast outflow detected in H.
Conclusions. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate
that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
A giant galaxy in the young Universe with a massive ringSérgio Sacani
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, dif- fuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understand- ing of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive col- lisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.
High-resolution UV/Optical/IR Imaging of Jupiter in 2016–2019Sérgio Sacani
Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53
days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field
Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14
filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging
approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm.
We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and
NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant
evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm
eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning
flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near
35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show
consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data.
Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the
15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of
the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The
HST data maps multiple concentric polar hoods of high-latitude hazes.
Observation of Bose–Einstein condensates in an Earth-orbiting research labSérgio Sacani
Quantum mechanics governs the microscopic world, where low mass and momentum
reveal a natural wave–particle duality. Magnifying quantum behaviour to
macroscopic scales is a major strength of the technique of cooling and trapping
atomic gases, in which low momentum is engineered through extremely low
temperatures. Advances in this feld have achieved such precise control over atomic
systems that gravity, often negligible when considering individual atoms, has
emerged as a substantial obstacle. In particular, although weaker trapping felds
would allow access to lower temperatures1,2
, gravity empties atom traps that are too
weak. Additionally, inertial sensors based on cold atoms could reach better
sensitivities if the free-fall time of the atoms after release from the trap could be made
longer3
. Planetary orbit, specifcally the condition of perpetual free-fall, ofers to lift
cold-atom studies beyond such terrestrial limitations. Here we report production of
rubidium Bose–Einstein condensates (BECs) in an Earth-orbiting research laboratory,
the Cold Atom Lab. We observe subnanokelvin BECs in weak trapping potentials with
free-expansion times extending beyond one second, providing an initial
demonstration of the advantages ofered by a microgravity environment for
cold-atom experiments and verifying the successful operation of this facility. With
routine BEC production, continuing operations will support long-term investigations
of trap topologies unique to microgravity4,5
, atom-laser sources6
, few-body physics7,8
and pathfnding techniques for atom-wave interferometry9–12
Quase 900 galáxias próximas, porém escondidas, têm sido estudadas por uma equipe internacional de astrônomos, levando uma nova luz sobre o entendimento do Grande Atrator - uma concentração difusa de massa a 250 milhões de anos-luz de distância, que está puxando a nossa Via Láctea, e milhares de outras galáxias em sua direção.
Usando o Multibeam Receiver, instalado no rádio telescópio Parkes de 64 m, pertencente à instituição CSIRO na Austrália, a equipe foi capaz de ver através das estrelas e da poeira da nossa galáxia, vasculhando assim uma região inexplorada do espaço, conhecida pelos astrônomos como Zone of Avoidance (Zona de Anulação).
“Nós descobrimos 883 galáxias, um terço das quais nunca tinham sido vistas anteriormente”, disse o Professor Lister Staveley-Smith, membro da equipe, do ARC Centre of Excellence for All-sky Astrophysics, e da University of Western Australia, um dos nós do International Centre for Radio Astronomy Research.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
The discovery of_lensed_radio_and_x-ray_sources_behind_the_frontier_fields_cl...Sérgio Sacani
We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster
MACSJ0717.5+3745. MACSJ0717.5+3745 offers the largest contiguous magnified area of any known cluster,
making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0–6.5 GHz
JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the
HST imaging. Within this sample, we find sevenlensed sources with amplification factors larger than two. None of
these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are
likely star-forming galaxies with star-formation rates (SFRs) of 10–50 M: yr−1 located at 1 1 z 1 2. Two of the
lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic
nuclei, given their 2–10 keV X-ray luminosities of ∼1043–44 erg s−1. From the derived radio luminosity function, we
find evidence for an increase in the number density of radio sources at 0.6 z 2.0, compared to a z 0.3 sample.
Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with
SFRs as low as ∼10Me yr−1, at the peak of cosmic star formation history.
Imaging the dust_sublimation_front_of_a_circumbinary_diskSérgio Sacani
Aims. We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust.
Methods. A very rich interferometric data set in six spectral channels was acquired of IRAS 08544-4431 with the new RAPID camera
on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the H-band was reconstructed
by combining the data of all spectral channels using the SPARCO method.
Results. We spatially separate all the building blocks of the IRAS 08544-4431 system in our milliarcsecond-resolution image. Our
dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an
unexpected flux signal of 4% from the secondary star. The energy output from this companion indicates the presence of a compact
circum-companion accretion disk, which is likely the origin of the fast outflow detected in H.
Conclusions. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate
that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
A giant galaxy in the young Universe with a massive ringSérgio Sacani
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, dif- fuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understand- ing of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive col- lisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.
High-resolution UV/Optical/IR Imaging of Jupiter in 2016–2019Sérgio Sacani
Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53
days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field
Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14
filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging
approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm.
We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and
NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant
evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm
eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning
flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near
35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show
consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data.
Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the
15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of
the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The
HST data maps multiple concentric polar hoods of high-latitude hazes.
Observation of Bose–Einstein condensates in an Earth-orbiting research labSérgio Sacani
Quantum mechanics governs the microscopic world, where low mass and momentum
reveal a natural wave–particle duality. Magnifying quantum behaviour to
macroscopic scales is a major strength of the technique of cooling and trapping
atomic gases, in which low momentum is engineered through extremely low
temperatures. Advances in this feld have achieved such precise control over atomic
systems that gravity, often negligible when considering individual atoms, has
emerged as a substantial obstacle. In particular, although weaker trapping felds
would allow access to lower temperatures1,2
, gravity empties atom traps that are too
weak. Additionally, inertial sensors based on cold atoms could reach better
sensitivities if the free-fall time of the atoms after release from the trap could be made
longer3
. Planetary orbit, specifcally the condition of perpetual free-fall, ofers to lift
cold-atom studies beyond such terrestrial limitations. Here we report production of
rubidium Bose–Einstein condensates (BECs) in an Earth-orbiting research laboratory,
the Cold Atom Lab. We observe subnanokelvin BECs in weak trapping potentials with
free-expansion times extending beyond one second, providing an initial
demonstration of the advantages ofered by a microgravity environment for
cold-atom experiments and verifying the successful operation of this facility. With
routine BEC production, continuing operations will support long-term investigations
of trap topologies unique to microgravity4,5
, atom-laser sources6
, few-body physics7,8
and pathfnding techniques for atom-wave interferometry9–12
Quase 900 galáxias próximas, porém escondidas, têm sido estudadas por uma equipe internacional de astrônomos, levando uma nova luz sobre o entendimento do Grande Atrator - uma concentração difusa de massa a 250 milhões de anos-luz de distância, que está puxando a nossa Via Láctea, e milhares de outras galáxias em sua direção.
Usando o Multibeam Receiver, instalado no rádio telescópio Parkes de 64 m, pertencente à instituição CSIRO na Austrália, a equipe foi capaz de ver através das estrelas e da poeira da nossa galáxia, vasculhando assim uma região inexplorada do espaço, conhecida pelos astrônomos como Zone of Avoidance (Zona de Anulação).
“Nós descobrimos 883 galáxias, um terço das quais nunca tinham sido vistas anteriormente”, disse o Professor Lister Staveley-Smith, membro da equipe, do ARC Centre of Excellence for All-sky Astrophysics, e da University of Western Australia, um dos nós do International Centre for Radio Astronomy Research.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
Carbon star formation as seen through the non-monotonic initial–final mass re...Sérgio Sacani
The initial–final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While
the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved.
A new analysis of a few carbon–oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR,
located over a range of initial masses, 1.65 ≲Mi
/M⊙ ≲ 2.10. The kink’s peak in white dwarf mass of about 0.70−0.75 M⊙ is
produced by stars with Mi≈ 1.8−1.9 M⊙, corresponding to ages of about 1.8−1.7 Gyr. Interestingly, this peak coincides with
the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and
intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation
in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their
impact on the spectrophotometric properties of galaxies.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
A rare case of FR I interaction with a hot X-ray bridge in the A2384 galaxy c...Sérgio Sacani
Clusters of varying mass ratios can merge and the process significantly disturbs
the cluster environments and alters their global properties. Active radio galaxies are
another phenomenon that can also affect cluster environments. Radio jets can interact
with the intra-cluster medium (ICM) and locally affect its properties. Abell 2384
(hereafter A2384) is a unique system that has a dense, hot X-ray filament or bridge
connecting the two unequal mass clusters A2384(N) and A2384(S). The analysis of its
morphology suggests that A2384 is a post-merger system where A2384(S) has already
interacted with the A2384(N), and as a result hot gas has been stripped over a ∼ 1
Mpc region between the two bodies. We have obtained its 325 MHz GMRT data,
and we detected a peculiar FR I type radio galaxy which is a part of the A2384(S).
One of its radio lobes interacts with the hot X-ray bridge and pushes the hot gas in
the opposite direction. This results in displacement in the bridge close to A2384(S).
Based on Chandra and XMM-Newton X-ray observations, we notice a temperature and
entropy enhancement at the radio lobe-X-ray plasma interaction site, which further
suggests that the radio lobe is changing thermal plasma properties. We have also
studied the radio properties of the FR I radio galaxy, and found that the size and
radio luminosity of the interacting north lobe of the FR I galaxy are lower than those
of the accompanying south lobe.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287Sérgio Sacani
Binary black hole (BH) central engine description for the unique blazar OJ 287 predicted that the
next secondary BH impact-induced bremsstrahlung flare should peak on 2019 July 31. This prediction
was based on detailed general relativistic modeling of the secondary BH trajectory around the primary
BH and its accretion disk. The expected flare was termed the Eddington flare to commemorate the
centennial celebrations of now-famous solar eclipse observations to test general relativity by Sir Arthur
Corresponding author: Lankeswar Dey
lankeswar.dey@tifr.res.in
arXiv:2004.13392v1 [astro-ph.HE] 28 Apr 2020
2 Laine et al.
Eddington. We analyze the multi-epoch Spitzer observations of the expected flare between 2019 July
31 and 2019 September 6, as well as baseline observations during 2019 February–March. Observed
Spitzer flux density variations during the predicted outburst time display a strong similarity with
the observed optical pericenter flare from OJ 287 during 2007 September. The predicted flare appears
comparable to the 2007 flare after subtracting the expected higher base-level Spitzer flux densities at
3.55 and 4.49 µm compared to the optical R-band. Comparing the 2019 and 2007 outburst lightcurves
and the previously calculated predictions, we find that the Eddington flare arrived within 4 hours of
the predicted time. Our Spitzer observations are well consistent with the presence of a nano-Hertz
gravitational wave emitting spinning massive binary BH that inspirals along a general relativistic
eccentric orbit in OJ 287. These multi-epoch Spitzer observations provide a parametric constraint
on the celebrated BH no-hair theorem.
A thirty-four billion solar mass black hole in SMSS J2157–3602, the most lumi...Sérgio Sacani
From near-infrared spectroscopic measurements of the Mg II emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1 , yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z > 4.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Evidence for an intermediate-mass black hole in the globular cluster NGC 6624Sérgio Sacani
PSR B1820−30A is located in the globular cluster NGC 6624 and is the closest known pulsar
to the centre of any globular cluster. We present more than 25 yr of high-precision timing
observations of this millisecond pulsar and obtain four rotational frequency time derivative
measurements. Modelling these higher order derivatives as being due to orbital motion, we find
solutions that indicate the pulsar is in either a low-eccentricity (0.33 e 0.4) smaller orbit
with a low-mass companion (such as a main-sequence star, white dwarf, neutron star or stellar
mass black hole) or a high-eccentricity (e 0.9) larger orbit with a massive companion. The
cluster mass properties and the observed properties of 4U 1820−30 and the other pulsars in
the cluster argue against the low-eccentricity possibility. The high-eccentricity solution reveals
that the pulsar is most likely orbiting around an intermediate-mass black hole (IMBH) of mass
>7500 M located at the cluster centre. A gravitational model for the globular cluster, which
includes such a central BH, predicts an acceleration that is commensurate with that measured
for the pulsar. It further predicts that the model-dependent minimum mass of the IMBH is
∼60 000 M. Accounting for the associated contribution to the observed period derivative
indicates that the γ -ray efficiency of the pulsar should be between 0.08 and 0.2. Our results
suggest that other globular clusters may also contain central BHs and they may be revealed by
the study of new pulsars found sufficiently close to their centres.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
Carbon star formation as seen through the non-monotonic initial–final mass re...Sérgio Sacani
The initial–final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While
the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved.
A new analysis of a few carbon–oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR,
located over a range of initial masses, 1.65 ≲Mi
/M⊙ ≲ 2.10. The kink’s peak in white dwarf mass of about 0.70−0.75 M⊙ is
produced by stars with Mi≈ 1.8−1.9 M⊙, corresponding to ages of about 1.8−1.7 Gyr. Interestingly, this peak coincides with
the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and
intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation
in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their
impact on the spectrophotometric properties of galaxies.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
A rare case of FR I interaction with a hot X-ray bridge in the A2384 galaxy c...Sérgio Sacani
Clusters of varying mass ratios can merge and the process significantly disturbs
the cluster environments and alters their global properties. Active radio galaxies are
another phenomenon that can also affect cluster environments. Radio jets can interact
with the intra-cluster medium (ICM) and locally affect its properties. Abell 2384
(hereafter A2384) is a unique system that has a dense, hot X-ray filament or bridge
connecting the two unequal mass clusters A2384(N) and A2384(S). The analysis of its
morphology suggests that A2384 is a post-merger system where A2384(S) has already
interacted with the A2384(N), and as a result hot gas has been stripped over a ∼ 1
Mpc region between the two bodies. We have obtained its 325 MHz GMRT data,
and we detected a peculiar FR I type radio galaxy which is a part of the A2384(S).
One of its radio lobes interacts with the hot X-ray bridge and pushes the hot gas in
the opposite direction. This results in displacement in the bridge close to A2384(S).
Based on Chandra and XMM-Newton X-ray observations, we notice a temperature and
entropy enhancement at the radio lobe-X-ray plasma interaction site, which further
suggests that the radio lobe is changing thermal plasma properties. We have also
studied the radio properties of the FR I radio galaxy, and found that the size and
radio luminosity of the interacting north lobe of the FR I galaxy are lower than those
of the accompanying south lobe.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287Sérgio Sacani
Binary black hole (BH) central engine description for the unique blazar OJ 287 predicted that the
next secondary BH impact-induced bremsstrahlung flare should peak on 2019 July 31. This prediction
was based on detailed general relativistic modeling of the secondary BH trajectory around the primary
BH and its accretion disk. The expected flare was termed the Eddington flare to commemorate the
centennial celebrations of now-famous solar eclipse observations to test general relativity by Sir Arthur
Corresponding author: Lankeswar Dey
lankeswar.dey@tifr.res.in
arXiv:2004.13392v1 [astro-ph.HE] 28 Apr 2020
2 Laine et al.
Eddington. We analyze the multi-epoch Spitzer observations of the expected flare between 2019 July
31 and 2019 September 6, as well as baseline observations during 2019 February–March. Observed
Spitzer flux density variations during the predicted outburst time display a strong similarity with
the observed optical pericenter flare from OJ 287 during 2007 September. The predicted flare appears
comparable to the 2007 flare after subtracting the expected higher base-level Spitzer flux densities at
3.55 and 4.49 µm compared to the optical R-band. Comparing the 2019 and 2007 outburst lightcurves
and the previously calculated predictions, we find that the Eddington flare arrived within 4 hours of
the predicted time. Our Spitzer observations are well consistent with the presence of a nano-Hertz
gravitational wave emitting spinning massive binary BH that inspirals along a general relativistic
eccentric orbit in OJ 287. These multi-epoch Spitzer observations provide a parametric constraint
on the celebrated BH no-hair theorem.
A thirty-four billion solar mass black hole in SMSS J2157–3602, the most lumi...Sérgio Sacani
From near-infrared spectroscopic measurements of the Mg II emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1 , yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z > 4.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Evidence for an intermediate-mass black hole in the globular cluster NGC 6624Sérgio Sacani
PSR B1820−30A is located in the globular cluster NGC 6624 and is the closest known pulsar
to the centre of any globular cluster. We present more than 25 yr of high-precision timing
observations of this millisecond pulsar and obtain four rotational frequency time derivative
measurements. Modelling these higher order derivatives as being due to orbital motion, we find
solutions that indicate the pulsar is in either a low-eccentricity (0.33 e 0.4) smaller orbit
with a low-mass companion (such as a main-sequence star, white dwarf, neutron star or stellar
mass black hole) or a high-eccentricity (e 0.9) larger orbit with a massive companion. The
cluster mass properties and the observed properties of 4U 1820−30 and the other pulsars in
the cluster argue against the low-eccentricity possibility. The high-eccentricity solution reveals
that the pulsar is most likely orbiting around an intermediate-mass black hole (IMBH) of mass
>7500 M located at the cluster centre. A gravitational model for the globular cluster, which
includes such a central BH, predicts an acceleration that is commensurate with that measured
for the pulsar. It further predicts that the model-dependent minimum mass of the IMBH is
∼60 000 M. Accounting for the associated contribution to the observed period derivative
indicates that the γ -ray efficiency of the pulsar should be between 0.08 and 0.2. Our results
suggest that other globular clusters may also contain central BHs and they may be revealed by
the study of new pulsars found sufficiently close to their centres.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
We've all heard that "change is coming", and "the need to change", but how do we practically achieve it? Join Adrian G. Simmons as he shares tools and mental hacks he’s collected in the process of re-engineering his own firm the last four years — bits of software, new habits, and perspective shifts, that have made the difference between just thinking about change, and actually being able to accomplish it. You can then apply these techniques and tools to whatever change you’re facing, to bring it to life.
Shared in November 2015 at Sleetercon in Las Vegas, Nevada.
Presented by Lee Ann Jackson, Counsellor, Agriculture and Commodities Division, World Trade Organization (WTO), at the Geneva Launch of IFPRI's 2016 Global Food Policy Report, April 12, 2016. More info: http://www.ifpri.org/event/geneva-launch-ifpris-2016-global-food-policy-report
Amélioration de la rétention : ce que 70 tests utilisateurs nous ont appris.Ferpection
Dans le cadre des AppDays, nous avons animé l'atelier suivant : "Amélioration de la rétention : ce que 70 tests utilisateurs nous ont appris".
Orientée application, cette présentation met en lumière les principales difficultés rencontrées par les utilisateurs au niveau UX.
Agile Brazil 2016 - Scaling without Expanding: a DevOps StoryVinicius Linck
When your business starts to grow, specially in terms of popularity you will realize that you need to scale with a minimum level of agility, specially on IT software industry. Communication starts to be crucial to keep your workflow in a good shape and agile methodologies are part of your company DNA. But probably you are still feeling that something is missing and you don’t have the control about all project streams, right? So DevOps is the next step for you.
Through automation techniques DevOps culture removes the barriers between your teams and break company silos to make the communication flow smooth and keep the project development mainline focused on get things done without wasting time on repetitive bits and tasks.
Atlassian tools were build for automation and productivity. The integration capabilities among the stack and with several market solutions allows any company to break those walls and scale the business without expanding the teams. You can evolve from a CI/CD pipeline stage and start to define ChatOps and Tracking strategies, bringing the support team closer to the development team and creating a trust and transparency environment between your company and the customers.
The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflectio...Sérgio Sacani
We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event
AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy
hosting a≈107 Me black hole (MBH inferred from host galaxy scaling relations). High-cadence Swift and Neutron
Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first
undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δt≈272 days during
which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δt = 264 days, harder
state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the
iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of -
+ 6.0 % 3.8 L 10.4
Edd when the X-ray
spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical
luminosity stays relatively constant, and the optical spectra are featureless. We propose the following
interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically
dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical
depth (∼a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger
column density—the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the
thermal–viscous instability in the inner accretion flow, leading to a much thinner disk.
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
Artigo descreve estudo feito por astrônomos e com a ajuda da sonda WISE da NASA para identificar as galáxias do tipo ELIRGs, entre elas a mais luminosa galáxia do universo, com um buraco negro gigantesco em seu interior e localizada a cerca de 12.8 bilhões de anos de distância da Terra.
Radio imaging obserations_of_psr_j1023_0038_in_an_lmxb_stateSérgio Sacani
Uma estrela super densa formada depois da explosão de uma supernova está expelindo poderosos jatos de material no espaço, sugerem pesquisas recentes.
Num estudo publicado no dia 6 de Agosto de 2015, uma equipe de cientistas na Austrália e na Holanda descobriram poderosos jatos sendo expelidos de uma sistema estelar duplo conhecido como PSR J1023+0038.
Pensava-se anteriormente que os únicos objetos no universo capazes de formar jatos poderosos eram os buracos negros.
O sistema PSR J1023+0038 contém uma estrela extremamente densa que os astrônomos chamam de estrela de nêutrons, numa órbita próxima com uma estrela normal.
Ela foi identificada primeiro como uma estrela de nêutrons em 2009, mas foi somente quando a equipe de pesquisa observou a estrela com o rádio telescópio Very Large Array nos EUA em 2013 e 2014 que eles perceberam que a estrela estava produzindo jatos mais fortes do que se esperava.
Os astrônomos James Miller-Jones, do International Centre for Radio Astronomy Research (ICRAR), disse que as estrelas de nêutrons podem ser pensadas como cadáveres estelares.
“Elas são formadas quando uma estrela massiva esgota todo o seu combustível e vira uma supernova, e as partes centrais da estrela colapsam sobre sua própria gravidade”, disse ele.
“Essas coisas tem normalmente entre uma vez e meia a massa do Sol e somente entre 10 a 15 km de diâmetro, de modo que são extremamente densas”.
Matter ejections behind the highs and lows of the transitional millisecond pu...Sérgio Sacani
Transitional millisecond pulsars are an emerging class of sources linking low-mass X-ray binaries to millisecond radio pulsars in
binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active
state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray
to optical pulsations are observed only during the high mode. Knowledge of the root reason for this puzzling behaviour remains
elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar
prototype, PSR J1023+0038, covering from radio to X-rays. The campaign was carried out over two nights in June 2021, and involved
12 different telescopes and instruments including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA and FAST.
By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by
changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on
top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with A
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
Observational constraints on mergers creating magnetism in massive starsSérgio Sacani
Massive stars (those ≥8 solar masses at birth) have radiative envelopes that cannot sustain the dynamos that produce magnetic fields in lower mass stars. Despite this, ∼7% of massive stars have observed magnetic fields. We use multi-epoch interferometric and spectroscopic observations to characterise a magnetic binary system formed of two massive stars. We find that only one star of the binary is magnetic. Using the non-magnetic star as an independent reference clock to estimate the age of the system, we show that the magnetic star appears younger than its companion. The system properties, and a surrounding bipolar nebula, can be reproduced by a model in which this system was originally a triple within which two of the stars merged, producing the magnetic massive star. Thus, our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers.
A Spatially Resolved Analysis of Star Formation Burstiness by Comparing UV an...Sérgio Sacani
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields
(UVCANDELS) program provides Hubble Space Telescope (HST)/UVIS F275W imaging for four CANDELS
fields. We combine this UV imaging with existing HST/near-IR grism spectroscopy from 3D-HST+AGHAST to
directly compare the resolved rest-frame UV and Hα emission for a sample of 979 galaxies at 0.7 < z < 1.5,
spanning a range in stellar mass of 108−11.5 Me. Using a stacking analysis, we perform a resolved comparison
between homogenized maps of rest-UV and Hα to compute the average UV-to-Hα luminosity ratio (an indicator of
burstiness in star formation) as a function of galactocentric radius. We find that galaxies below stellar mass of
∼109.5 Me, at all radii, have a UV-to-Hα ratio higher than the equilibrium value expected from constant star
formation, indicating a significant contribution from bursty star formation. Even for galaxies with stellar mass
109.5 Me, the UV-to-Hα ratio is elevated toward their outskirts (R/Reff > 1.5), suggesting that bursty star
formation is likely prevalent in the outskirts of even the most massive galaxies, but is likely overshadowed by their
brighter cores. Furthermore, we present the UV-to-Hα ratio as a function of galaxy surface brightness, a proxy for
stellar mass surface density, and find that regions below ∼107.5 Me kpc−2 are consistent with bursty star formation,
regardless of their galaxy stellar mass, potentially suggesting that local star formation is independent of global
galaxy properties at the smallest scales. Last, we find galaxies at z > 1.1 to have bursty star formation, regardless of
radius or surface brightness.
Triple Spiral Arms of a Triple Protostar System Imaged in Molecular LinesSérgio Sacani
Most stars form in multiple-star systems. For a better understanding of their formation processes, it is important to
resolve the individual protostellar components and the surrounding envelope and disk material at the earliest
possible formation epoch, because the formation history can be lost in a few orbital timescales. Here we present
Atacama Large Millimeter/submillimeter Array observational results of a young multiple protostellar system,
IRAS 04239+2436, where three well-developed large spiral arms were detected in the shocked SO emission.
Along the most conspicuous arm, the accretion streamer was also detected in the SO2 emission. The observational
results are complemented by numerical magnetohydrodynamic simulations, where those large arms only appear in
magnetically weakened clouds. Numerical simulations also suggest that the large triple spiral arms are the result of
gravitational interactions between compact triple protostars and the turbulent infalling envelope.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Similaire à Frontier fields clusters_chandra_and_jvla_view_of_the_pre_m_erging_cluster_macs_j0416_1_2403 (20)
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
ISI 2024: Application Form (Extended), Exam Date (Out), EligibilitySciAstra
The Indian Statistical Institute (ISI) has extended its application deadline for 2024 admissions to April 2. Known for its excellence in statistics and related fields, ISI offers a range of programs from Bachelor's to Junior Research Fellowships. The admission test is scheduled for May 12, 2024. Eligibility varies by program, generally requiring a background in Mathematics and English for undergraduate courses and specific degrees for postgraduate and research positions. Application fees are ₹1500 for male general category applicants and ₹1000 for females. Applications are open to Indian and OCI candidates.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptxRASHMI M G
Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
2. 2. Acceleration by hadronic collisions: Inelastic collisions
between CR protons trapped in the gravitational potential
of a cluster (e.g., originating from supernova explosions,
active galactic nuclei (AGNs) outbursts, previous merger
events, etc.) and thermal ICM protons give rise to a
secondary population of CR electrons, which conse-
quently are visible at radio frequencies (e.g., Blasi &
Colafrancesco 1999; Dolag & Enßlin 2000).
However, hybrid models have also been postulated, in which
radio halos may be produced by turbulent reacceleration of
secondary particles resulting from hadronic proton–proton
collisions (Brunetti & Blasi 2005; Brunetti & Lazarian 2011).
The radio halos predicted by hybrid models are expected to be
found in more relaxed clusters and to be underluminous for the
masses of the hosting clusters (see also Brunetti & Jones 2014,
for a review).
Hadronic radio halo models predict that magnetic fields
should either be different in clusters with and without halos, or
that gamma-ray emission should be detected in clusters hosting
halos (e.g., Jeltema & Profumo 2011). However, there is no
evidence that magnetic fields are stronger in clusters with radio
halos (e.g., Bonafede 2010), and there has been no conclusive
gamma-ray detection with the Fermi telescope (Ackermann
et al. 2010). Therefore, current observational evidence
disfavors hadronic models.
A textbook example of a merging cluster with a bright radio
halo is the famous Bullet cluster, 1E 0657-56 (Elvis et al. 1992;
Liang et al. 2000; Markevitch et al. 2002; Shimwell et al.
2014). Chandra has revealed that this system has a bullet-like
subcluster core moving through the disturbed ICM of the main
cluster (Markevitch et al. 2002). Immediately ahead of the core
there is a density discontinuity associated with a cold front,
while further out in the same direction there is a density
discontinuity associated with a shock front (Markevitch et al.
2002; Owers et al. 2009). Recently, another shock front has
been found on the opposite side of the Bullet cluster, behind the
bullet-like core (Shimwell et al. 2015). Chandra observations
of the Bullet cluster were followed up with optical/lensing data
acquired, most notably, with the Very Large Telescope and the
Hubble Space Telescope (HST). Chung et al. (2010) have
shown that the redshift distribution of the Bullet cluster is
bimodal, with two redshift peaks at z ∼ 0.21 and z ∼ 0.35,
which imply a velocity difference ∼3000 km s−1
between the
two merging subclusters. The gravitational lensing analysis has
shown that the Bullet cluster is a dissociative merger, in which
the essentially collisionless DM (σDM < 0.7 g cm−2
, Randall
et al. 2008b) has decoupled from the collisional ICM
(Markevitch et al. 2004; Randall et al. 2008b). Lage & Farrar
(2014) have combined the X-ray and lensing data with
numerical simulations to constrain the merger scenario of the
Bullet cluster.
Here, we present results from Chandra, Jansky Very Large
Array (JVLA), and Giant Metrewave Radio Telescope
(GMRT) observations of another merging galaxy cluster: the
HST Frontier Fields22
cluster MACS J0416.1-2403 (z = 0.396,
Ebeling et al. 2001; Mann & Ebeling 2012). Optical and
lensing studies of this cluster have been presented recently by,
e.g., Zitrin et al. (2013, 2015), Schirmer et al. (2015), Jauzac
et al. (2014), Grillo et al. (2015). Most recently, Jauzac et al.
(2015) mapped the DM distribution of this merging system
using strong- and weak-lensing data. Their analysis revealed
two mass concentrations associated with the two main
subclusters involved in the merger, plus two smaller X-ray-
dark mass structures NE and SW of the cluster center. Jauzac
et al. (2015) combined their lensing data with archival Chandra
observations to study the offsets between the DM and the gas
components. They report good DM-gas alignment for the NE
subcluster, but a significant offset for the SW one. Based on the
spectroscopic, lensing, and X-ray results, Jauzac et al. (2015)
proposed two possible scenarios for the merger event in MACS
J0416.1-2403—one pre-merging and one post-merging—but
were unable to distinguish between the two.
The analysis presented herein combines significantly deeper
Chandra observations with recently acquired JVLA and
GMRT data and with the optical/lensing results reported by
Jauzac et al. (2015) to improve our understanding of the merger
event in MACS J0416.1-2403. The Chandra JVLA, and
GMRT observations and data reduction procedures are
described in Section 2. In Section 3 we discuss the background
analysis of the Chandra data, and in Sections 4–7 we present
the X-ray results. The radio results are presented in Section 8.
In Section 9 we use the deeper Chandra data to revise the DM-
gas offsets reported by Jauzac et al. (2015). In Section 10 we
discuss the implications of our findings for the merger scenario
of MACS J0416.1-2403. In Section 11 we examine the origin
of the radio halo. A summary of our results is provided in
Section 12.
Throughout the paper we assume a ΛCDM cosmology with
H0 = 70 km s−1
Mpc−1
, ΩM = 0.3, and ΩΛ = 0.7. At the
redshift of the cluster, 1′ corresponds to approximately 320 kpc.
Unless stated otherwise, the errors are quoted at the 90%
confidence level.
2. OBSERVATIONS AND DATA REDUCTION
2.1. Chandra
The HST Frontier Fields cluster MACS J0416.1-2403 was
observed with Chandra for 324 ks between 2009 June and
2014 December. A summary of the observations is given in
Table 1.
The data were reduced using CIAO v4.7 with the calibration
files in CALDB v4.6.5. The particle background level of the
VFAINT observations was lowered by filtering out CR events
associated with significant flux in the 16 border pixels of the
5 × 5 event islands. Soft proton flares were screened out from
all observations using the deflare routine, which is based on the
lc_clean code written by M. Markevitch. The flare screening
was done using an off-cluster region at the edges of the field of
view (FOV), which was selected to include only pixels located
at distances greater than 2.5 Mpc from the cluster center and
to exclude any point sources detectable by eye. The clean
exposure times following this cleaning are listed in Table 1.
The inspection of an ObsID 10446 spectrum extracted from
an off-cluster region showed a significant high-energy tail,
which indicates that this observation is contaminated by flares
that were not detected by the filtering routine. Given the
relatively short exposure time of this observation, we decided
to exclude ObsID 10446 from our analysis rather than attempt
to model the flare component.
We reprojected the other five observations to a common
reference frame, and created merged images in the energy
bands 0.5–2, 0.5–3, 0.5–4, 0.5–7, and 2–7 keV. The exposure-22
http://www.stsci.edu/hst/campaigns/frontier-fields/
2
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
3. corrected, vignetting-corrected 0.5–4 keV mosaic image is
shown in Figure 1. To detect point sources, we also created
merged exposure map-weighted point-spread function images
(ECF = 90%) in each of the five energy bands. Point sources
were detected in the individual bands with the CIAO task
wavdetect, using the merged maps, wavelet scales of 1, 2, 4, 8,
16, and 32 pixels, a sigma threshold of 5 × 10−7
, and ellipses
with 5σ axes. A few additional point sources that were missed
by wavdetect were selected by eye and excluded from the data.
All point sources detected by wavdetect were excluded from
the data very conservatively, using the elliptical region that
covered the largest area among the five elliptical regions
identified for the different energy bands.
2.2. JVLA
JVLA observations of MACS J0416.1-2403 were obtained
in the L-band in the BnA, CnB, and DnC array configurations.
The observations were recorded with the default wide-band
L-band setup, giving 16 spectral windows each having 64
Table 1
Chandra Observations
ObsID Observing Mode CCDs On Starting Date Total Time Clean Time
(ks) (ks)
10446 VFAINT 0, 1, 2, 3, 6 2009 Jun 07 15.8 15.8
16236 VFAINT 0, 1, 2, 3, 6 2014 Aug 31 39.9 38.6
16237 FAINT 0, 1, 2, 3, 6 2013 Nov 20 36.6 36.3
16304 VFAINT 0, 1, 2, 3, 6 2014 Jun 10 97.8 95.2
17313 VFAINT 0, 1, 2, 3, 6 2014 Nov 28 62.8 59.9
16523 VFAINT 0, 1, 2, 3, 6 2014 Dec 19 71.1 69.1
Figure 1. Logarithmic-scaled Chandra surface brightness map of the HST Frontier Fields Cluster MACS J0416.1-2403, in the energy band 0.5–4 keV. The image was
binned by a factor of 4 (1 pixel ≈2″), exposure-corrected, vignetting-corrected, and smoothed with a 2D Gaussian kernel of width 1 pixel × 1 pixel. The large image
shows the mosaic of all the ObsIDs summarized in Table 1, while the top image zooms in on the brightest X-ray regions of the cluster, in a region of size
2.9 × 2.9 Mpc2
. The dashed gray circle marks the boundary of the R500 region of the cluster. Green crosses mark the centers of the dark matter halos of the NE and
SW merging clusters (M. Jauzac 2015, private communication).
3
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
4. channels, covering the entire 1–2 GHz band. An overview of
the observations is given in Table 2.
The data were calibrated with the Common Astronomy
Software Applications (CASA) package version 4.2.1 (McMul-
lin et al. 2007). As a first step we flagged data affected by radio
frequency interference (RFI) using AOFlagger (Offringa et al.
2010), after correcting for the bandpass shape. Data affected by
other problems and antenna shadowing were flagged as well.
After flagging, we applied the pre-determined elevation
dependent gain tables and antenna offset positions. The data
were Hanning smoothed.
We determined initial gain solutions using 10 channels at the
center of the spectral windows for the primary calibrators
3C147 and 3C138. We then re-calibrated the bandpass and
obtained delay terms (gaintype = ‘‘K’’) using the
unpolarized calibrator 3C147. A next step consisted of
calibration of the cross-band delays
(gaintype = ‘‘KCROSS’’) using the polarized calibrator
3C138. We then solved again for the gains on the primary
calibrators but now using all channels. The channel dependent
leakage corrections were found using 3C147 and the polariza-
tion angles were set using 3C138. The gains were again re-
determined for all calibrator sources which included the phase
calibrator J0416-1851. Finally, the flux density-scale was
bootstrapped from the primary calibrators to J0416-1851 and
the calibration solutions were applied to the target field.
To refine the calibration for the target field, we performed
three rounds of phase-only self-calibration and two final rounds
of amplitude and phase self-calibration. W-projection (Corn-
well et al. 2005, 2008) was employed during the imaging,
taking the non-coplanar nature of the array into account. The
self-calibration was independently performed for the three
different data sets from the different array configurations. The
full bandwidth was imaged using MS-MFS clean (nterms = 2;
Rau & Cornwell 2011). Briggs (1995) weighting with a
robust factor of −0.75 was used for self-calibration. Clean
masks were used, which were made with the PyBDSM source
detection package (Mohan & Rafferty 2015). The value of the
chosen robust parameter was a compromise between
sensitivity and approximately matching the GMRT resolution
(see the next subsection).
After the self-calibration, the three data sets were combined.
One final round of self-calibration was carried out on the
combined data set. The final images were corrected for the
primary beam attenuation.
In addition, we imaged the data set using an inner uv-range
cut of 4.3 kλ (corresponding to a scale of about 1′, or 320 kpc)
and robust = 0 weighting. This model was then subtracted
from the visibility data to allow a search for diffuse emission in
the cluster. We imaged the data set with the emission from
compact sources subtracted using a Gaussian uv-taper of
20″ and employing multi-scale clean (Cornwell 2008). An
overview of the resulting image properties, such as root mean
square (rms) noise and resolution are given in Table 3.
2.3. GMRT
GMRT 610 MHz data for MACS J0416.1-2403 were
collected on 2013 December 3, using 26 antennas. The on-
source time was 5.0 hr, and a total bandwidth of 33.3 MHz (RR
correlations only), split into 512 channels, was recorded.
NRAOʼs Astronomical Image Processing System (AIPS) was
used to carry out the initial calibration of the visibility data set.
The primary calibrator 3C 147 was used to set the flux density
scale and derive the bandpass solutions for all the antennas.
The source J0409-179 was observed for 6-minutes scans at
intervals of ∼25 minutes and used as the secondary phase and
gain calibrator. About 20% of the data, mostly from short
baselines, were affected by RFI and subsequently flagged. Gain
solutions were obtained for the calibrator sources and together
with the bandpass solutions applied to the target field. In total,
480 of the 512 channels were used; the rest of the channels
were discarded as they were too noisy due to the bandpass roll-
off. The 480 channels were averaged down to 48 channels to
reduce the size of the data.
The visibility data were then imported into CASA to refine
the calibration via the process of self-calibration. Three rounds
of phase-only self-calibration and two final rounds of amplitude
and phase self-calibration were applied. The phase-only self-
calibration was carried out on a 30 s timescale. The amplitude
and phase self-calibration was carried out on a 2 minute
timescale, pre-applying the phase-only solutions before solving
for the amplitude and phases on the longer 2 minute timescale.
We employed W-projection during the imaging and used
nterms = 2.
A map with Briggs (robust = 0.5) weighting of the field
was produced, which resulted in a resolution of 7 6 × 4 0 and
an rms noise level of 54 μJy beam−1
(Table 3). Similarly to the
JVLA L-band data reduction, we imaged the data set using an
inner uv-range cut of 4.3 kλ to obtain a model of the compact
sources in the field. After subtracing this model from the uv-
data, we re-imaged with uniform weighting and a Gaussian uv-
taper to obtain a beam size of 20″.
2.4. VLITE
A new commensal observing system called the VLA Low
Band Ionospheric and Transient Experiment (VLITE)23
has
been developed for the NRAO JVLA (Clarke et al. 2015, in
preparation) and was operational during the observations of
MACS J0416.1-2403. The VLITE correlator is a custom
designed DiFX software correlator (Deller et al. 2011). The
system processes 64 MHz of bandwidth centered on 352 MHz
with two second temporal resolution and 100 kHz spectral
resolution. VLITE operates during nearly all pointed JVLA
observations with primary science goals at frequencies above
1 GHz, providing data simultaneously for 10 JVLA antennas
using the low band receiver system (Clarke et al. 2011).
Table 2
JVLA L-band Observations
BnA-array CnB-array DnC-array
Observation dates 2014 Jan 25 2015 Jan 12 2014 Sep 19
Frequency cover-
age (GHz)
1–2 1–2 1–2
On source time (hr) 0.6 3.2 1.5
Correlations full stokes full stokes full stokes
Channel width (MHz) 1 1 1
Visibility integration
time (s)
2 3 5
23
http://vlite.nrao.edu/
4
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
5. We processed the CnB configuration VLITE observation of
MACS J0416.1-2403 from 2015 January 12 using a combina-
tion of the Obit software package (Cotton 2008) and AIPS (van
Moorsel et al. 1996). VLITE data at frequencies ν > 360 MHz
were removed due to the presence of strong RFI from a satellite
downlink that is present during most operations. The data at
ν < 360 MHz were flagged using the AIPS program RFLAG to
remove the majority of the remaining RFI. The bandpass was
flattened using observations of several calibrators taken near
the time of the observations (3C48, 3C138, 3C147, and
3C286). These calibrator sources were taken in the same
primary observing band as MACS J0416.1-2403. The delays
were determined using these same calibrators. The delay
corrected data then were flux calibrated using these same
calibrator sources. No phase calibrator is required for low band
observations due to the large FOV (FWHM ∼2°.3 at 320 MHz)
and typical presence of sufficiently strong sources in the field
that allow for self-calibration.
The initial imaging of the target field revealed additional RFI
that was identified in the residual data set after all compact
sources had been subtracted from the uv data. These baselines
were excised from the full data set and we further refined the
calibration through four rounds of phase-only self-calibration.
Non-coplanar effects were taken into account in the imaging
steps using small facets to make a fly-eye image of the full field
out to the FWHM with additional facets placed on bright
sources out to 20° from the field center. Data were imaged
using small clean masks placed around all sources. The final
VLITE image of MACS J0416.1-2403 has a resolution of
45 7 × 31 1 and an rms noise of 2.0 mJy beam−1
. The image
was made using a Briggs robust parameter of 0 (see Table 3).
3. X-RAY FOREGROUND AND
BACKGROUND MODELING
We analyzed the Chandra data using the Group F stowed
background event files, which are appropriate for observations
taken after 2009 September 21. The particle background was
subtracted from the data, while the foreground and background
sky components were modeled from off-cluster regions. For
each of the cluster ObsIDs, we created corresponding stowed
background event files, applied the VFAINT cleaning to those
associated with cluster observations taken in this observing
mode, and renormalized the stowed background observations
such that the count rates in the energy band 10–12 keV
matched those of the corresponding observation in the same
energy band. We modeled the sky components as the sum of
unabsorbed thermal emission from the Local Hot Bubble
(LHB; APEC component with T ≈ 0.1 keV; Snowden 1998),
absorbed thermal emission from the Galactic Halo (GH; APEC
component with T ≈ 0.2 keV; Henley et al. 2010), and
absorbed non-thermal emission from undetected point sources
in the FOV (power-law component with index 1.41 ± 0.06; De
Luca & Molendi 2004). The redshifts of the foreground
components were set to 0, while the abundances were set to
solar values assuming the abundance table of Anders &
Grevesse (1989). The hydrogen column density was fixed to
2.89 × 1020
atoms cm−2
(Kalberla et al. 2005). The Chandra
spectra were fit in the energy band 0.5–7 keV using XSPEC
v12.8.2—the lower limit was chosen to avoid calibration
uncertainties at low energies, and the upper limit to increase the
signal-to-noise ratio (S/N).
When fitting the Chandra spectra in the energy band
0.5–7 keV, the ∼0.1 keV LHB component cannot be con-
strained. Instead, we constrain this component using a
ROentgen SATellite (ROSAT) All-Sky Survey (RASS) spec-
trum24
corresponding to an annulus with radii 0°.15 and 1°.0
around the cluster. The ROSAT spectrum was fit in the energy
band 0.1–2.4 keV, with the normalization of the power-law
background component fixed to 8.85 × 10−7
photons keV−1
cm−2
s−1
arcmin−2
(Moretti et al. 2003). The temperatures and
normalizations of the LHB and GH components were free in
the fit. The results of the fit to the ROSAT spectrum are
presented in Table 4.
Based on the ROSAT results, the parameters of the LHB
components were fixed for the Chandra spectra. The five
Chandra spectra were then fitted in parallel, assuming that they
are described by the same foreground model. The power-law
normalizations, on the other hand, were left to vary
independently, in order to account for the varying exposure
time across the merged observation that was used for point
source detection. The energy sub-band 0.5–0.8 keV was
ignored for ObsID 16237 due to negative spectral residuals
caused by a change in the spectral shape of the background
component that is not filtered by the VFAINT cleaning, which
occurred between 2009 (the date of the Group F background
files) and 2013 (the date of the observation; A. Vikhlinin 2015,
private communication). The subtraction of the instrumental
background resulted in small line residuals near the spectral
positions of the Al Kα (E ≈ 1.49 keV), Si Kα (E ≈ 1.75 keV),
and Au Mα, β (E ≈ 2.1 keV) fluorescent instrumental lines.
Therefore, we excluded from the spectra very narrow bands
(ΔE = 0.10 keV) surrounding these lines.
The best-fitting foreground and background parameters are
summarized in Table 4. The spectra were grouped to have at
least 1 count per bin, and the fit was done using the extended
C-statistic25
(Cash 1979; Wachter et al. 1979).
Table 3
Radio Imaging Parameters
Instrument Weighting Resolution rms Noise
(arcsec × arcsec) (μJy beam−1
)
JVLA 1.5 GHz Briggs −0.75 7.8 × 5.5 14
JVLA 1.5 GHz uniform +20″ Gaussian taper 18 × 18 20
GMRT 610 MHz Briggs 0.5 7.6 × 4.0 54
GMRT 610 MHz uniform +20″ Gaussian taper 20 × 20 360
VLITE 340 MHz Briggs 0.0 45.7 × 31.1 2000
24
https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/xraybg/xraybg.pl
25
https://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/
XSappendixStatistics.html
5
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
6. 4. GLOBAL X-RAY PROPERTIES
MACS J0416.1-2403 has been previously identified as a
merging galaxy cluster at z = 0.396 (Mann & Ebeling 2012).
The brightness of the NE subcluster core is significantly more
peaked than that of the SW subcluster, which instead has a
rather flat brightness distribution (Figure 1).
We determined the average cluster temperature by extracting
spectra from a circular region of radius 1.2 Mpc (approximately
R500, Sayers et al. 2013) centered at α = 4h
16m
08 8 and
δ = −24° 04′ 14 0 (J2000). The spectra extracted from the five
Chandra ObsIDs were fit in parallel, assuming the cluster
emission is described by a single-temperature thermal compo-
nent.26
For this global fit, the sky background parameters
were fixed to the values listed in Table 4, and the redshift
was fixed to 0.396. We found T 10.06 0.49
0.50
keV and
L 7.43 0.08 10X, 0.1 2.4 keV
44( ) erg s−1
. The average
cluster parameters are shown in Table 5.
5. MAPPING THE CLUSTERʼS X-RAY PROPERTIES
5.1. Mapping of the ICM Temperature
We mapped the cluster properties using CONTBIN (Sanders
2006).27
The merged Chandra image was adaptively binned in
regions of ∼3600 source plus sky background counts in the
energy band 0.5–7 keV. The bins follow the surface brightness
contours of the cluster, thus minimizing possible gas mixing in
bins located near density discontinuities. Instrumental back-
ground and total spectra were extracted from regions
corresponding to each bin, and grouped to have at least one
count per bin. The net spectra were modeled as the sum of sky
background components plus a single temperature absorbed
thermal model (phabs×APEC) with free temperature and
normalization. The metallicity was fixed to Z Z0.24 (see
Section 4). The sky background emission was fixed to the
model summarized in Table 4. The spectra extracted from the
five Chandra data sets were fitted in parallel, with the
temperatures and normalizations linked between the different
ObsIDs. The fits were done using the extended C-statistic. The
resulting temperature map is shown in Figure 2.
The temperature is high throughout the cluster, which causes
the uncertainties on the measurements to be high. The
temperature map does not show significant structure. Within
the uncertainties, the temperatures out to ∼400 kpc from the
cluster center are consistent with ∼10 keV.
5.2. Mapping of the ICM Pressure and Entropy
The electron number density can be derived either from the
model normalization of the fitted spectrum, or from the surface
brightness in the regions of interest. Extracting the number
density from either of these quantities requires assumptions
about the cluster geometry. Here, we estimated the electron
number density from the surface brightness; we note that our
results are unchanged when deriving the density from the
spectral normalization.
The surface brightness, ζ, is essentially proportional to the
emission measure,
n dl 1e
2
( )
where the integration is done along the line of sight and ne is
the electron number density. More accurately, the surface
brightness is also temperature-dependent. This dependence
introduces an uncertainty of 10% in the pressure and entropy
maps, which is less than the uncertainties on the temperatures
and does not affect our results.
Table 4
Foreground and Background Spectral Models
Chandra ROSAT
Component Ta b
Ta b
LHB 0.10 ± 0.01c
9.32 100.83
0.62 7c
0.10 ± 0.01 9.32 100.83
0.62 7
GH 0.25 0.08
0.23
2.35 101.66
4.20 7 0.22 0.04
0.05
6.74 102.06
3.44 7
Power-law
L 4.20 100.73
0.86 7
L L
ObsID 16236
Power-law
L 2.17 100.86
0.76 7
L L
ObsID 16237
Power-law
L 2.45 100.59
0.60 7
L L
ObsID 16304
Power-law
L 3.70 100.84
0.86 7
L L
ObsID 17313
Power-law
L 4.33 100.69
0.71 7
L L
ObsID 16523
Notes.
a
Temperature, in units of keV.
b
Normalization, in units of cm−5
arcmin−2
for the thermal components, and in units of photons keV−1
cm−2
s−1
arcmin−2
for the non-thermal components.
c
Fixed parameter.
Table 5
Cluster Properties in R500
T (keV) 10.06 0.49
0.50
Z (Z ) 0.24 0.04
0.05
L erg sX,0.1 2.4 keV
1( ) (7.43 ± 0.08) × 1044
26
We tried adding an additional thermal component to fit the cluster emission,
but the parameters of the second component could not be constrained.
27
We also created temperature maps using the codes described by Churazov
et al. (2003) and Randall et al. (2008a), and obtained consistent results at the
90% confidence level.
6
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
7. We approximated the density as ζ1/2
, and defined the
pseudo-pressure and pseudo-entropy as:
P T , 20.5 2 keV
1 2
( )
K T . 30.5 2 keV
1 3
( )
The pseudo-pressure and pseudo-entropy maps are included in
Figure 2.
Strong jumps in pressure and entropy would indicate the
presence of strong density discontinuities in the ICM.
However, neither the pressure map, nor the entropy map of
MACS J0416.1-2403 shows evidence of such strong jumps
between the regions. We note that while a pressure and entropy
discontinuity can be seen between regions #3 and #0, the size
of region #0 is too large for this result to truly indicate that
there is a density discontinuity at the boundary of the two
regions.
In Table 6 we list the best-fitting temperatures, spectral
normalizations, and 0.5–2 keV count rates for the regions in
Figure 2. The bin numbers necessary to relate Table 6 and
Figure 2 are shown in Figure 3. An interactive version of the
temperature map, which combines Figures 2, 3 and Table 6
is available at http://hea-www.cfa.harvard.edu/~gogrean/
interactive/MACSJ0416_Tmap.html.
6. PROPERTIES OF THE INDIVIDUAL SUBCLUSTERS
The merging history of the individual subclusters is closely
related to their degree of disturbance. In the following two
sections, we perform the imaging analysis of the NE and SW
subclusters in order to characterize their merging states. For
both subclusters, we created surface brightness profiles in
sectors centered on the respective X-ray peaks, and attempted
to model the profiles with isothermal β-models (Cavaliere &
Fusco-Femiano 1976, 1978):
S r S
r
r
1 40
c
2 3 0.5
( ) ( )
⎡
⎣
⎢
⎢
⎛
⎝
⎜
⎞
⎠
⎟
⎤
⎦
⎥
⎥
where S0 is the central surface brightness, rc is the core radius,
β is the beta parameter, and r is the radius from the cluster
center.
Simple β-models provide good descriptions of the X-ray
profiles of galaxy clusters that do not have strong ICM
temperature gradients (e.g., Ettori 2000a, 2000b). Based on
Figure 2, there are indeed no strong temperature gradients in
the NE and the SW subclusters of MACS J0416.1-2403.
Before fitting, all the profiles were binned to a minimum of 1
count/bin. The fits used Cash statistics. Fitting was done using
a modified version of the PROFFIT package28
(Eckert
et al. 2011). All the surface brightness profiles presented in
the following subsections are in the energy band 0.5–4 keV.
The profiles were instrumental background-subtracted, and
exposure- and vignetting-corrected.
6.1. NE Subcluster
The sector used to create the surface brightness profile of the
NE subcluster and the fits to this profile are shown in Figure 4.
The sky background surface brightness level was determined
by fitting a constant to the outer bins (radii 5 0–10 7) of the
profile. The sky background level was kept fixed in the
following fits. The very central part of the profile is
significantly underestimated by the best-fitting β-model.
Figure 2. Temperature, pseudo-pressure, and pseudo-entropy maps of MACS J0416.1-2403. In all maps, black elliptical regions mark the regions from which point
sources have been removed.
Table 6
Best-fitting Temperatures, Normalizations, and 0.5–2 keV Count Rates
for the Regions in Figure 3
Bin Number Ta b
SX
c
0 7.95 0.92
1.32
(2.24 ± 0.06) × 10−5
(7.39 ± 0.07) × 10−6
1 10.74 1.37
2.10
(1.70 ± 0.05) × 10−4
(3.38 ± 0.06) × 10−5
2 13.25 2.32
3.07
(2.31 ± 0.07) × 10−4
(4.34 ± 0.08) × 10−5
3 10.32 1.35
1.91
(2.77 ± 0.08) × 10−4
(5.30 ± 0.09) × 10−5
4 11.69 1.46
2.10
(1.63 ± 0.05) × 10−3
(2.96 ± 0.06) × 10−4
5 9.73 1.24
1.52
(9.80 ± 0.29) × 10−4
(1.84 ± 0.04) × 10−4
6 15.39 2.87
3.42
(9.03 ± 0.23) × 10−4
(1.62 ± 0.03) × 10−4
7 12.90 2.15
3.64
(7.13 ± 0.22) × 10−4
(1.27 ± 0.03) × 10−4
8 12.18 1.90
2.41
7.10 100.21
0.22 4 (1.31 ± 0.03) × 10−4
9 11.43 1.65
2.29
(5.51 ± 0.17) × 10−4
(1.02 ± 0.02) × 10−4
10 8.41 0.90
1.37
(4.12 ± 0.13) × 10−4
(8.02 ± 0.15) × 10−5
Notes.
a
Temperature, in units of keV.
b
Spectral normalization, in units of cm arcmin .5 2
c
0.5–2 keV count rate, in units of photons cm s arcmin .2 1 2
28
Available upon request.
7
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
8. Instead, the profile is described better by a double β-model:
S r S
r
r
1 . 5
i
i
i1,2
0,
c,
2 3 0.5
( ) ( )
⎡
⎣
⎢
⎢
⎛
⎝
⎜
⎞
⎠
⎟
⎤
⎦
⎥
⎥
Double β-models provide good representations of cooling-core
clusters (e.g., Jones & Forman 1984; Ota et al. 2013).
However, the core of the NE subcluster in MACS J0416.1-
2403 is far from cool, having a temperature >10 keV based on
the temperature map in Figure 2. To constrain a possible cooler
component, we examined the possibility that the projected
temperature of the gas in bin #4 (see Figure 3) is increased due
to the projection of hot gas onto the subcluster core. We
modeled the spectrum of bin #4 with a two-temperature APEC
model: one describing possible cool gas in the cluster center,
and another describing hotter gas (T > 10 keV) in the cluster
outskirts. The normalizations of the two components were free
in the fit. The count statistics do not allow us to leave both
temperatures free in the fit. Therefore, we left the temperature
of the hot plasma free, and fixed the temperature of the core to
5 keV.29
In the best-fitting model, the normalization of the cool
component is about 5 times lower than that of the hot
component, which implies that the gas density in the core is
lower than the density right outside the core radius; such a
density model is not physical. The two-temperature APEC
model also provides no improvement in the statistics of the fit.
If the core has a temperature <5 keV, then the normalization of
the cool component would be even lower relative to the
normalization of the hot component, so the core density would
be even lower.
Cooler gas in the NE core could be masked by inverse
Compton (IC) emission from the AGN hosted by the NE
subcluster brightest cluster galaxy (BCG). To examine this
possibility, we measured the temperature in an annulus with
radii 32 and 64 kpc around the AGN in the NE BCG. The best-
fitting temperature in this annulus is very high, 15.65 3.22
5.03
keV.
In a smaller circle with a radius of 35 kpc around the NE core,
the best-fitting temperature is 10.54 2.11
3.00
keV, and consistent
with the temperature calculated in an annulus around the core.
Therefore, we find no evidence that the NE core is cool.
From the best-fitting double β-model, we calculated the
central density of the NE core to be (1.4 ± 0.3) × 10−2
cm−3
.
The density and temperature of the NE core hence imply a
cooling time of 3.5 0.9
1.0
Gyr, which further supports our
conclusion that the NE subcluster cannot be classified as a
cool core cluster based on currently available X-ray data.
To investigate if the double β-model shape of the NE profile
is caused by substructure in a particular direction, we divided
the NE sector shown in Figure 4 into three subsectors, and
modeled the profile of each subsector with β- and double β-
models. The fits are shown in Figure 5. For each of the
subsectors, a double β-model describes the profile better than a
single β-model at a confidence level >99.99%.
6.2. SW Subcluster
The surface brightness profile of the SW subcluster and the
sector used in the extraction of this profile are shown in
Figure 6. As for the NE profiles, the sky background profile
was modeled by fitting a constant to the outer bins of the
profile, in the range r = 4 5–10 7. Unlike the NE profiles, the
SW profile is modeled well by a simple β-model. The fit is
shown in Figure 6.
A weak edge in the profile can be seen at r ∼ 1 5. We
divided the profile into three subsectors with equal opening
angles (60°) to check whether the edge is seen along all three
directions, and found that it is present only in the central
subsector (position angles 280°–340°, measured from the W in
a counterclockwise direction). To describe it, we fitted a
projected broken power-law elliptical density model to the
surface brightness profile between r = 0 5–4 0. The density
Figure 3. Left: The map shows the association of regions in Figure 2 with the fit values in Table 6. Numbers are region numbers. Black ellipses mark the regions
where point sources have been removed. Right: Same surface brightness map as in Figure 1, with overlaid regions used for mapping the physical properties of
the ICM.
29
A larger temperature would be unusual for a cool core.
8
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
9. model is defined as:
n r
C n
r
r
r r
n
r
r
r r
, if
, if
, 6
0
d
d
0
d
d
( ) ( )
⎧
⎨
⎪
⎪
⎩
⎪
⎪
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
where n is the electron number density, n0 is the density
immediately ahead of the density jump, C is the density
compression, r is the distance from the center of the sector, rd
is the radius at which the density jump is located, and α and β
are the indices of the two power-laws. The fit is shown in
Figure 7. If the density discontinuity is a shock front, then its
magnitude corresponds to a shock with Mach number
1.40 .0.12
0.14
Unfortunately, the count statistics are
too poor to allow us to distinguish between a cold front and
a shock front based on the temperature jump, and thus
we cannot determine the nature of the surface brightness
edge.
7. SUBSTRUCTURE IN THE ICM
The search for substructure in the ICM is motivated by the
identification in the lensing maps of two less massive
structures in addition to the main NE and SW subclusters
(Jauzac et al. 2015). The positions of these mass structures are
shown in Figure 8 and denoted by S1 and S2 for consistency
with the notation of Jauzac et al. (2015). In the analysis
of Jauzac et al. (2015), S1 and S2 were found to be X-ray-
dark; however, the X-ray data presented here are ∼6 times
deeper, which would make it easier to observe ICM
substructure.
We searched for substructure using the unsharp-masked
image of the cluster, which was created by dividing the
difference of two 0.5–4 keV fluxed images convolved with
Gaussians of widths 4″ and 10″ by their sum. The resulting
image, shown in Figure 8, highlights substructure on scales
of ∼20–50 kpc.30
There is no excess X-ray emission at the
positions of S1 and S2. However, the emission is elongated in
the direction of both mass structures. In the south, the ICM
appears elongated in the direction of S1, while in the north
the emission is elongated along the line connecting the NE
and SW subclusters and then appears to curve in the direction
of S2. We note that if S1 and S2 have already merged
with the NE and SW subclusters, the DM would have
decoupled from the gas, and therefore we do not necessarily
expect a spatial overlap between the DM and gas
components.
Interestingly, the unsharp-masked image enchances a small
cavity with a diameter ∼50 kpc NW of the core of the NE
subcluster. We examined the significance of the cavity from
the azimuthal surface brightness profile in an annulus around
the cluster center. The annulus was divided in 14 partial
annuli with equal opening angles. The partial annuli and the
azimuthal surface brightness profile are shown in Figure 9.
The azimuthal surface brightness profile is lowest in four
partial annuli located NW of the NE core. The largest dip is in
the partial annulus that crosses the middle of the X-ray cavity
seen in the unsharp-masked image; the opening angles of this
Figure 4. Top: Sector used to model the surface brightness of the NE
subcluster. Annuli are drawn only to guide the eye and do not reflect the actual
bin size used for the surface brightness profiles. Middle: β-model fit to the
surface brightness profile of the NE subcluster. For clarity, the profile shown in
this plot was binned to a uniform signal-to-noise ratio of 5. Bottom: Double β-
model fit to the surface brightness profile of the NE subcluster. The individual
β-models are shown with dashed lines. For clarity, the profile shown in this plot
was binned to a have 200 counts per bin. The best-fitting model parameters are
listed in the middle and bottom plots; radii units are arcmin, and surface
brightness units are photon cm−2
s−1
arcmin−2
. Fixed parameters are shown
with a superscripted †. The bottom panel shows the residuals of the fit.
30
Smoothing with Gaussians of larger widths does not reveal additional
substructure.
9
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
10. partial annulus are 51°–77°. No radio emission fills the X-ray
cavity, but the cavity was likely inflated by the AGN hosted
by the NE BCG (see Section 8).
8. RADIO RESULTS
The JVLA 1–2 GHz images reveal several compact sources
in the cluster region (Figure 10). Two of these sources are
Figure 5. β-model (left) and double β-model (right) fits to the surface brightness profiles of the NE sectors with position angles of 45°–115° (top), 115°–155°
(middle), and 155°–225° (bottom). The position angles are measured from W, in a counterclockwise direction. For all the profiles, a double β-model constitutes a
better fit than a single β-model, with confidence levels of 4.4σ for the top profile, 3.3σ for the middle profile, and 6.4σ for the bottom profile. The individual β-models
are shown with dashed lines. For clarity, all profiles shown have been regrouped in the plots to have 200 counts per bin. The best-fitting model parameters are listed on
the plots; radii units are arcmin, and surface brightness units are photon cm−2
s−1
arcmin−2
. Fixed parameters are shown with a superscripted †. The bottom panel
shows the residuals of the fit.
10
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
11. associated with cD galaxies in the NE and SW subclusters.
These sources are also detected in the GMRT 610 MHz image
(Figure 11). These two point-like AGN have 1.5 GHz
integrated flux densities31
of 1.47 ± 0.08 (NE) and 0.27 ±
0.03 (SW) mJy. At 610 MHz we measure flux densities of 3.24
± 0.34 (NE) and 0.33 ± 0.07 (SW) mJy for these sources.
Using these fluxes, we compute spectral indices of α = –0.88
± 0.13 (NE) and α = –0.22 ± 0.27 (SW), which are typical for
AGN (e.g., Prandoni et al. 2009).
We also find diffuse extended emission in the cluster. The
diffuse emission reveals itself in the JVLA image as an increase
in the “noise” in the general cluster area. This diffuse emission
is better visible in our low-resolution tapered image with
emission from compact sources subtracted (Figure 10). The
diffuse emission has a elongated shape measuring about
120″ × 45″ (0.65 by 0.24 Mpc) and is oriented along a NE-
SW axis, following the overall distribution of the X-ray
emission. We also find evidence for this diffuse emission in the
Figure 6. Top: Sector used to model the surface brightness of the SW
subcluster. Annuli are drawn only to guide the eye and do not reflect the actual
bin size used for the surface brightness profiles. Bottom: β-model fit to the
surface brightness profile of the SW subcluster. For clarity, the profile shown in
this plot was binned to have 200 counts per bin. The best-fitting model
parameters are listed; radii units are arcmin, and surface brightness units are
photon cm−2
s−1
arcmin−2
. Fixed parameters are shown with a superscripted †.
The bottom panel shows the residuals of the fit.
Figure 7. Broken power-law model fit to the surface brightness profile of the
SW subcluster in a subsector with position angles 280°–340°, measured from
the W in counterclockwise direction. For clarity, the profile shown in this plot
was binned to have 80 counts per bin. The best-fitting model parameters are
listed; radii units are arcmin, and surface brightness units are photon cm−2
s−1
arcmin−2
. Fixed parameters are shown with a superscripted †.
Figure 8. Unsharp-masked X-ray image of MACS J0416.1-2403, created by
dividing the difference of two 0.5–4 keV fluxed images convolved with
Gaussians of widths 4″ and 10″ by their sum. Point sources have not been
subtracted from this image, and there are some residuals surrounding them. The
positions of the two less massive mass structures identified by Jauzac et al.
(2015) are marked as S1 and S2 with circles of diameters 100 kpc, as also done
by Jauzac et al. (2015). Black crosses mark the centers of the DM halos of the
two main subclusters (M. Jauzac 2015, private communication). The dashed
arc shows the position of the density discontinuity detected near the SW
subcluster. The location of the X-ray cavity is also marked.
31
The errors on the flux measurements include the absolute flux calibration
uncertainty and the uncertainty based on the map noise, taking the integration
area into account. The uncertainties were added in quadrature. For the JVLA,
we assumed a 5% uncertainty for the absolute flux scale bootstrapped from the
primary calibrator sources. For the GMRT observations, we assumed an
uncertainty in the absolute flux scale of 10%.
11
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
12. GMRT 610 MHz image, although less clearly than in the JVLA
1.5 GHz image (Figure 11). In the low-resolution tapered
GMRT image there is again evidence for diffuse emission, but
the peak flux is only at a level of 3σrms.
For the integrated flux of the diffuse emission, we measure
1.60 ± 0.14 mJy (at 1.5 GHz) in an ellipse with radii of 70″ by
40″ oriented with a position angle of 45° (following the overall
brightness distribution). From the GMRT tapered image, we
estimate an integrated 610 MHz flux of 6.8 ± 3.0 mJy for the
diffuse emission in the same area. We evaluated the accuracy of
the compact source subtraction and conclude that this does not
add significantly to the uncertainty on the radio halo flux.
Based on the residuals visible for the brightest source in the
field, we find that the compact source subtraction was
performed at a level better than 0.5%.
Taking the two flux measurements at 1.5 and 0.61 GHz, we
obtain a spectral index of 1.6 0.51500
610
for the diffuse
emission. Based on the above results, we compute a radio
power of P 1.3 0.3 101.4 GHz
24( ) W Hz−1
, scaling with
the spectral index of α = –1.6 ± 0.5.32
VLITE shows emission co-incident with the NE subcluster
where the higher resolution 1–2 GHz images (Figure 10) reveal
the compact sources and the brightest portion of the diffuse
emission. We fit the 320–360 MHz VLITE emission with a
single Gaussian component to measure the integrated flux. We
measure a total flux of 20.5 ± 7.0 mJy, where we have included
a 13% uncertainty in the source flux, as determined for a low
Figure 9. Left: Unsharp-masked image as in Figure 8, with overlaid partial annuli used to evaluate the azimuthal surface brighness profile around the NE core. Right:
Azimuthal surface brightness profile around the NE core. The largest dip in the profile is in the direction of the cavity seen in the unsharp-masked image, between
opening angles of 51°–77°. Angles are measured counterclockwise, starting from the W.
Figure 10. Left: JVLA 1–2 GHz high-resolution image showing the compact sources in the cluster region. Right: JVLA 1–2 GHz image of the radio halo, with
compact sources subtracted. Chandra contours are overlaid on both images. The contours are based on an exposure-corrected, vignetting-corrected image that was
smoothed with a Gaussian kernel of width 4″; they are drawn at [0.6, 1.3, 2.0, 2.7, K] × 10−7
photons cm−2
s−1
. Green crosses mark the centers of the DM halos.
Dashed blue lines show the 3 radio contours (these are only visible in the high-resolution radio image). The beam size is shown in the bottom left corner of the
images.
32
We included the spectral index uncertainty in the uncertainty on the radio
power.
12
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
13. signal-to-noise source in VLITE (Clarke et al. 2015, in
preparation). The VLITE emission contains both the diffuse
component and the compact emission from the two point
sources associated with the NE and SW clusters. We use the
VLA and GMRT flux measurements to determine the spectral
index of the two compact sources, assume that spectral index
extends to the central VLITE frequency, and estimate the
contribution to the total VLITE emission from the compact
sources. We subtract that from the VLITE flux and get an
estimate of the diffuse component detected by VLITE of 14.6
± 7.0 mJy. Comparing the VLITE flux to the JVLA flux, we
calculate a spectral index of 1.5 0.8.1500
340
The results
are consistent with the spectral index estimate from the GMRT
data. Deeper low-frequency data are required to better constrain
the spectral properties of the diffuse emission.
In the JVLA 1–2 GHz data we did not detect diffuse
polarized emission in the cluster in Stokes Q and U images we
made. Halos are generally unpolarized at the few percent level
or less so this result is not surprising (e.g., Feretti et al. 2012).
We note however, that a proper search for diffuse emission,
taking full advantage of the large bandwidth, would require
Faraday Rotation Measure Synthesis.
9. GAS-DM DECOUPLING
The combined X-ray and lensing analysis of Jauzac et al.
(2015) determined that the gas component of the SW subcluster
has decoupled from the DM component and lags behind the
subclusterʼs galaxies as it travels toward the NE subcluster.
In the NE subcluster, on the other hand, the DM and gas
components were determined by Jauzac et al. (2015) to
spatially overlap.33
Offsets between the DM and gas compo-
nents of merging galaxy clusters set crucial constraints on the
merger state. In particular, significant offsets indicate a post-
merging system, while a lack of offsets supports a pre-merging
scenario. Below, we discuss the DM-gas offsets in light of the
deeper Chandra data.
The centers of the DM halos of the two subclusters (M.
Jauzac 2015, private communication) are marked on Figure 12,
which shows an HST ACS/F814W image of the cluster, with
overlaid Chandra and JVLA contours. The centers of the X-ray
cores were defined as the peaks in the X-ray emission, and were
determined from the 0.5 to 4 keV Chandra surface brightness
map of the cluster, convolved with a Gaussian of σ = 4″. We
also considered the uncertainties on the surface brightness
distribution, and defined the uncertainties on the X-ray peaks as
the regions around the cores in which the X-ray brightness is
consistent (within the propagated Poisson errors on the counts
image) with the brightness of the corresponding peak. We note
that our approach only provides a lower limit on the extent of
the peak regions, because the background was included in the
surface brightness map used for this analysis. The uncertainties
on the DM centers are <1″, significantly smaller than the
uncertainties on the centers of the X-ray cores. In Figure 13, we
compare the position of the DM centers with that of the X-ray
peak regions. Rather than confirming the previously-reported
offset between the gas and DM components of the SW
subcluster, Figure 13 shows that both X-ray peaks are, within
the uncertainties, co-located with the DM centers. We speculate
that the discrepancy between the results presented herein and
those reported by Jauzac et al. (2015) is caused by a higher
noise level in the significantly shallower X-ray data used in
previous studies; our data is ≈6 times deeper, which is
equivalent to a reduction in noise by a factor of ≈2.5.
10. MERGER SCENARIO
Jauzac et al. (2015) showed that the galaxy redshift
distribution in MACS J0416.1-2403 is bimodal relative to the
mean redshift, with the SW subcluster (mean redshift 0.3966)
moving toward the observer and the NE subcluster (mean
redshift 0.3990) moving away from the observer. Based on
these observations, Jauzac et al. (2015) suggested two possible
merger scenarios:
1. MACS J0416.1-2403 is a pre-merging system, in which
the SW subcluster comes from behind the NE subcluster,
and is now seen near first core passage;
2. MACS J0416.1-2403 is a post-merging system, in which
the SW cluster approached the NE subcluster from above,
and is now seen near its second core passage.
We refer the reader to Figure 13 of Jauzac et al. (2015) for a
sketch of the two geometries. In this section, we try to
distinguish between the two scenariosusing our X-ray and radio
findings.
Figure 11. GMRT 610 MHz high-resolution image, showing the compact
radio sources. Overlaid in blue are GMRT 610 MHz contours of the diffuse
radio emission, drawn at 1.1 mJy/beam. JVLA 1–2 GHz radio contours
showing diffuse radio emission are drawn in magenta at [60, 80, 100, 120, 140,
160] μJy/beam. VLITE 340 MHz radio contours are drawn in orange at
10 mJy/beam. The ellipse shows the region in which the radio flux was
measured. Crosses mark the centers of the dark matter halos of the NE and SW
subclusters.
33
An analysis of the DM-gas offset in MACS J0416.1-2403 was carried out
more recently by Harvey et al. (2015). For the SW subcluster, their DM peak is
offset by about 100 kpc (∼20″) from the DM peak determined by previous
analyses (e.g., Grillo et al. 2015; Jauzac et al. 2015, models at https://archive.
stsci.edu/pub/hlsp/frontier/macs0416/models/). We do not understand the
cause of the offset, but choose to use the DM peaks determined by Jauzac et al.
(2015), because their locations are consistent within 2″ with the locations of the
DM peaks determined by other authors (e.g., Grillo et al. 2015). We also point
out that the peak of the galaxy distribution chosen by Harvey et al. (2015) for
the SW subcluster in MACS~J0416.1-2403 is strongly biased by a foreground
galaxy (z 0.10 ;0.08
0.12
Jouvel et al. 2014) at R.A. = 04: 16: 06.833 and
decl. = −24: 05: 08.40 that was not excluded from their analysis.
13
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
14. 10.1. Cooler Gas in the NE?
Approximately 300 kpc NE of the NE core, the temperature
maps show a region (region #10; T 8.41 0.90
1.37
keV) that is
cooler than the neighboring region closer to the cluster center
(region #8; T 12.18 1.90
2.41
). The cool gas in this region could
be pre-shock gas ahead of a shock front. We examined the
surface brightness profile across the cooler region, but could
not confirm a surface brightness discontinuity with a
confidence …90%. A density jump could be masked by
projection effects. Nonetheless, while the temperature differ-
ence between regions #8 and #10 is significant at 90%
confidence (but not at 2σ) and there is a pseudo-pressure jump
between the two regions, the lack of a clear density jump does
not allow us to confirm a shock front NE of the NE core.
10.2. No Gas-DM offset
In head-on binary mergers, the essentially collisionless DM
travels ahead of the collisional gas. There are several scenarios
that could explain the spatial overlap of the DM andthe gas in
MACS J0416.1-2403:
(i) In MACS J0416.1-2403, the NE and SW subclusters are
seen before first core passage and have yet to interact
strongly with each other (e.g., due to the subclusters still
being very far apart, and/or to the merger having a high
impact parameter). This scenario requires that the merger
axis is significantly inclined with respect to the plane of
the sky, because, in projection, the distance between the
subcluster cores is only ∼250 kpc.
Figure 12. HST ACS/F814W optical image of MACS J0416, with overlaid Chandra (left) and JVLA (right) contours. X-ray contours are the same as in Figure 10.
Radio contours are based on the JVLA image with the emission from compact sources subtracted using a Gaussian uv-taper of 20″. The JVLA contours are drawn at
[60, 80, 100, 120, 140, 160] μJ/beam. The centers of the DM halos of the NE and SW subclusters are marked with red crosses.
Figure 13. Chandra 0.5–4 keV surface brightness maps of the NE subcluster center (left) and of the SW subcluster center (right). The overexposed regions (in brown)
are the peak regions of the two subcluster cores. The position of the DM centers are marked with white crosses. The white “X” indicates the location of the X-ray peak
of the SW subcluster, as it was identified from shallower Chandra data by Jauzac et al. (2015).
14
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
15. (ii) The DM and gas in the NE and SW subclusters overlap
only in projection. This requires either that one of the
subclusters was essentially undisturbed by the merger and
our line of sight aligns with the trajectory of the other
subcluster, or that the subclusters’ trajectories are parallel
and both are aligned with our line of sight.
(iii) The NE and SW subclusters are seen after first core
passage, and the gas of the SW subcluster slingshot and
caught up with the DM halo, after they had separated near
pericenter.
The radial velocity difference between the BCGs of the NE
and SW subclusters was reported by Jauzac et al. (2015) to be
≈800 km s−1
. The sound speed in a cluster with a temperature
of ≈10 keV is ≈1300 km s−1
, and typical collision velocities
are 1–2 times the sound speed. Therefore, the radial velocity
difference between the two BCGs in MACS J0416.1-2403
seems rather low compared to typical collision velocities, and
supports a scenario in which the merger progresses outside the
plane of the sky, but the merger axis is not perpendicular to the
plane of the sky. Alternatively, the merger could be seen after
first core passage, near the turnaround point; this scenario
requires a merger axis that is almost perpendicular to the plane
of the sky.
10.3. Subcluster Morphology
The effects of ram pressure on the morphologies of two
merging clusters also provide clues on the merger scenario.
When two clusters merge, tails that trail the cluster cores may
form. In a post-merging system seen before turnaround, these
plasma tails are elongated toward the core of the opposite
subcluster core. In a pre-merging system, the tails are elongated
away from the opposite subcluster core. The two morphologies
are sketched in Figure 14. In MACS J0416.1-2403, tails are not
immediately seen in the surface brightness map. However, the
unsharp-masked image in Figure 8 reveals that both the NE and
the SW subclusters are trailed by tails whose directions are
consistent with a pre-merger scenario.
10.4. Substructure in the NE Core
The surface brightness profile of the NE subcluster cannot be
described by a single β-model, but instead by a double β-model
composed of a very compact core and a more extended gas
halo. Such a profile is typically used to model cool core clusters
(e.g., Jones & Forman 1984; Ota et al. 2013), but it can also
describe the surface brightness of merging clusters seen in
projection (e.g., Zuhone 2009; Machacek et al. 2010). The core
of the NE subcluster is very hot and has a long cooling time,
which disfavors the possibility that the NE subcluster hosts a
cool core. Instead, the observed substructure is more likely the
result of a merger event.
The most straight-forward scenario would be that the NE and
SW subclusters have already merged, and while the core of the
SW subcluster was destroyed in the collision, as evidenced by
the subclusterʼs flat surface brightness, the core of the NE
subcluster survived. Cool cores that survive a recent merger
event preserve part of their cold gas. However, we found no
evidence of cool gas in the NE core. Therefore, the NE core is
unlikley to be the remnant of a recent interaction between the
NE and SW subclusters.
An alternative scenario is that the NE subcluster is merging
with the DM halo S2 (Figure 8). However, S2 is not associated
with a concentration of galaxies, and thus is an unlikely
candidate for a group of galaxies (Jauzac et al. 2015). No other
mass concentration that the NE subcluster might be currently
merging with has been detected.
One other possibility, postulated by numerical simulations of
Poole et al. (2008), is that the NE subcluster underwent a
merger or a series of mergers over ∼1 Gyr ago, and while its
core has already relaxed back to a compact state, it has not yet
recooled. In this scenario, the merger could not have been with
the SW subcluster, because the two subclusters are involved in
an ongoing merger. Instead, the NE subcluster needs to have
interacted several Gyr ago with one or more clusters that are no
longer directly detectable in the X-ray maps, in the lensing
maps, or in the redshift distribution of the NE subcluster.
Alternatively, past mergers could also have heated the cool
core without destroying it, by inducing sloshing in the central
galaxy. The kinetic energy of the sloshing central galaxy would
then have been dissipated as heat between successive mergers
(ZuHone et al. 2010).
10.5. The AGN and the X-Ray Cavity in the NE Core
The collision velocity between the NE and SW subcluster is
unlikely to be highly supersonic. If the cluster is a post-merging
system, a cavity could have had enough time to form since first
core passage. However, given the short timescale and the
intense turbulence following the moment of first core passage,
forming a new cavity would require a strong AGN outburst.
The expectation would then be to observe radio emission
associated with the X-ray cavity. However, this radio emission
is not observed. Instead, the presence of an X-ray cavity NW of
the NE core supports a pre-merger scenario. The cavity was
most likely inflated by a recent weak outburst of the AGN
detected in the BCG of the NE subcluster.
Figure 14. Effects of ram pressure on the morphologies of two merging
clusters before first core passage (left) and after first core passage (right). The
contours used in the sketch are based on the XMM-Newton surface brightness
map of the group NGC 4839 infalling onto the Coma cluster.
15
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
16. 10.6. SW Density Discontinuity
The density discontinuity detected S of the SW subcluster is
located along the line connecting the NE subcluster, the SW
subcluster, and S1. The discontinuity also appears coincident
with the position of S1, but this could be a projection effect.
There are two scenarios that would explain the origin of the
density discontinuity: the merger of the SW subcluster with S1,
or the merger of the SW subcluster with the NE subcluster.
If the discontinuity were triggered by a merger between the
two main subclusters, then the merger must have already
progressed past the moment of the first core passage.
Furthermore, because the NE core is very compact and hosts
an X-ray cavity, it is unlikely that it was significantly affected
by a merger with the SW subcluster. Therefore, taking into
account the constraints set by the lack of an offset between the
gas and DM peaks of both subclusters, it is the SW subcluster
whose trajectory must be aligned with our line of sight. In this
geometry, a shock front would be expected ahead of the SW
subcluster (with respect to its direction of motion), i.e., our line
of sight should be perpendicular to the 3D shock “cap.”
Instead, however, the surface brightness discontinuity we
detect is seen in projection only S-SW of the SW subcluster. If
the detected density discontinuity is the appearance of the
shock in projection, then we would expect to observe it over a
larger angular opening. Most likely, the density discontinuity is
caused by the interaction of the SW subcluster with S1.
In conclusion, while we cannot completely eliminate the
possibility of MACS J0416.1-2403 being a post-merging
cluster, we believe the sum of our findings favors a pre-
merging scenario.
11. A NEWLY DISCOVERED RADIO HALO
We classify the diffuse radio emission in the cluster as a
halo, since the emission has low-surface brightness, large
extent, and is centrally located. With a largest linear size (LLS)
of 0.65 Mpc, the halo has a somewhat smaller size than other
radio halos in merging clusters, which have LSSs of
1–1.5 Mpc. (e.g., Feretti et al. 2012). However, the LLS is
larger than that of the radio mini-halos found in cool core
clusters (e.g., Burns et al. 1992; Gitti et al. 2007; Giacintucci
et al. 2014). Additionally, an important difference from mini-
halos is that neither the NE nor the SW subclusters contains a
cool core.Furthermore, as shown in Figure 12, the halo seems
to be associated with both subclusters. The halo in MACS
J0416.1-2403 is also rather elongated compared to most known
radio halos. However, there are other clusters with similarly
elongated radio halos (e.g., Bonafede et al. 2012; van Weeren
et al. 2012a, 2012b; Shimwell et al. 2014).
The radio emission around the northern subcluster contains
about a factor of 2 more flux than the emission around the
southern one. An interesting question is whether we observe a
single radio halo, caused by the merger between the NE and the
SW subclusters, or two individual halos belonging to the two
subclusters. In the latter case, these halos must have originated
from previous merger events within two subclusters them-
selves. This would make MACS J0416.1-2403 similar to the
case of the radio halo pair in Abell 399 and Abell 401 (Murgia
et al. 2010), with the difference that Abell 399/401 seems to be
at a much earlier pre-merger stage.
For radio halos, a correlation is observed between the
clusterʼs X-ray luminosity and the radio halo power (the L PX –
correlation), with the most X-ray luminous clusters correspond-
ing to the most powerful radio halos (e.g., Liang et al. 2000;
Enßlin & Röttgering 2002; Cassano et al. 2006). The X-ray
luminosity is used as a proxy of cluster mass. The distribution
in the L PX – plane is bimodal when clusters without halos are
included. Merging clusters with radio halos follow the L PX –
correlation, while the upper limits on the radio power of other
clusters are well below the correlation (Brunetti et al. 2007).
A correlation is also observed between the clusterʼs
integrated Sunyaev–Zel’dovich (SZ) effect (i.e., the integrated
Compton YSZ parameter) and the radio halo power (e.g.,
Basu 2012, 2013). YSZ is proportional to the volume integral of
the pressure. The SZ signal should be less affected by the
cluster dynamical state and therefore is expected to be a better
indicator of the clusterʼs mass. Basu (2012, 2013) and Cassano
et al. (2013) showed that there is good agreement between the
YSZ – P scaling relation and the scaling relations based on
X-ray data.
In Figure 15, we place MACS J0416.1-2403 on the L PX –
and Y PSZ – diagrams, with the values for the other clusters taken
from Cassano et al. (2013). The YSZ,500 value for the cluster was
recently calculated by Planck Collaboration et al. (2015), which
found Y 0.71 0.24 10SZ,500
4( ) Mpc2
. Specifically, this
is the value of YSZ,500 obtained from the union catalog based
on the MMF134
detection algorithm. We also computed
the value of YSZ,500 using the gNFW model fit to Bolocam
presented by Czakon et al. (2015) and obtained
Y 1.49 0.28 10SZ,500
4( ) Mpc2
. The difference between
the Planck and Bolocam measurements is not understood, but
is likely due to some combination of random noise fluctuations,
deviations from the assumed pressure profile used to extract
YSZ,500 (particularly at large radii), contamination from dust or
other astronomical signals, and calibration uncertainties.
Furthermore, we note that this cluster is not detected by
PowellSnakes—one of the three Planck algorithms—and the
values of YSZ,500 obtained from the other two algorithms
(MMF1 and MMF335
) are significantly different, perhaps
indicating that measurements of YSZ,500 toward this cluster
contain larger than typical systematic uncertainties. In
Figure 15, we plot both the Planck and Bolocam values of
Y .SZ,500
Interestingly, the radio halo power falls on the low end of the
L PX – correlationfor radio halos without ultra-steep spectra.
However, using the Planck measurement of Y ,SZ,500 we find
that the halo power is consistent with the expected Y PSZ –
correlation, indicating the halo is not underluminous for the
cluster mass. While the Bolocam value of YSZ,500 does imply
lower than expected halo power, the nominal Y PSZ – relation
used for comparison is derived solely from Planck SZ
measurements. We therefore consider our interpretation based
on the Planck value of YSZ,500 to be more robust. Given this
interpretation, MACS J0416.1-2403 could be just an outlier in
the L PX – diagram, based on the fact that there is significant
scatter in the correlations.
It is also possible that the X-ray luminosity of MACS
J0416.1-2403 is not a good indicator of the clusterʼs mass, and
the luminosity is boosted by the merger. A boost in X-ray
luminosity is predicted for approximately one sound-crossing
time, which for MACS J0416.1-2403 is ≈1 Gyr (Ricker &
Sarazin 2001). This boost would affect other clusters on the
34
Matched multi-filter algorithm, implementation 1.
35
Matched multi-filter algorithm, implementation 3.
16
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
17. correlation as well, but it could affect MACS J0416.1-2403
more since we are seeing a cluster close to first core passage.
The mass of the cluster in R500 is (7.0 ± 1.3) × 1014
Me
(Umetsu et al. 2014). Based on the scaling relations of Pratt
et al. (2009), the mass corresponds to a 0.1–2.4 keV cluster
luminosity of (1.1 ± 0.4) × 1045
erg s−1
, which is in agreement
with the luminosity calculated from the Chandra data.
Therefore, based on the M L500 500– scaling relation, we have
no indication that the cluster luminosity is higher than expected
for a cluster of this mass.
Another possibility is that we are seeing an ultra-steep
spectrum radio halo (α −1.5, Brunetti et al. 2008). In this
case, the radio halo is only underluminous at higher frequencies
(i.e., above a GHz), while the integrated flux density rapidly
increases at lower frequencies. Ultra-steep spectrum radio halos
are predicted by the turbulent re-acceleration model to form in
less energetic mergers (Brunetti et al. 2008). The mass of
MACS J0416.1-2403 is indeed near the lower end of the mass
range of clusters with radio halos (see, e.g., Cassano
et al. 2013, who list masses between 4.4 × 1014
Me and
1.7 × 1015
Me for clusters hosting radio halos). Some, but not
all clusters with masses similar to that of MACS J0416.1-2403
host ultra-steep spectrum radio halos. The steepness of the
radio spectrum is affected not only by the cluster mass though,
but also by the magnetic fields of the clusters and by the
particle acceleration efficiency; at the moment, these are not
known.
An ultra-steep spectrum radio halo is also expected in the
later phases of a merger, when the radio spectrum had time to
steepen due to synchrotron and IC losses (e.g., Donnert
et al. 2013). If the diffuse radio emission in MACS J0416.1-
2403 is ultra-steep and the steepness was caused by ageing,
then the emission in the cluster is in fact consisting of two
individual radio halos that were formed in the NE and SW
subclusters during previous mergers—possibly the same
mergers that heated the cluster cores.
Unfortuntely, the 320–360 MHz VLITE and 610 MHz
GMRT data presented in Section 8 are not sufficient to
confirm, or rule out, the presence of an ultra-steep spectrum
radio halo. Low-frequency GMRT (ν < 610 MHz) and/or deep
P-band JVLA observations are required to settle this case.
A third possibility is that we could be witnessing the first
stages of the formation of this radio halo. We do not think that
the radio halo is fading, because the NE and SW subclusters are
still in the process of merging and most likely they have not yet
undergone core passage (see Section 10). Therefore, when the
merger progresses further, the radio halo could brighten,
increase in size, and move onto the correlation.
12. SUMMARY
The HST Frontier Field cluster MACS J0416.1-2403
(z = 0.396) is a merging system that consists of two main
subclusters and two additional smaller mass structures (Jauzac
et al. 2015). Here, we presented results from deep Chandra
JVLA, and GMRT observations of the cluster. The main aims
of our analysis were to identify signatures of merger activity in
the ICM, constrain the merger scenario, and detect and
characterize diffuse radio sources. Below is a summary of
our main findings:
1. The cluster has an average temperature of 10.06 0.49
0.50
keV,
an average metallicity of 0.24 0.04
0.05
Ze, and a 0.1–2.4 keV
luminosity of L 7.43 0.08 10X
44( ) erg s−1
.
2. The NE subcluster has a very compact core and a nearby
X-ray cavity, but its temperature is very high (T ∼
10 keV), we find no evidence of multi-phase gas, and its
cooling time is 3 Gyr. The presence of a compact core
and of an X-ray cavity indicates that the NE subcluster
was not disrupted by a recent major merger event.
3. S-SW of the SW subcluster, there is a weak density
discontinuity that is best-fitted by a density compression
of 1.56 .0.29
0.38
The discontinuity is located along the line
connecting the NE subcluster, the SW subcluster, and the
mass structure S1 reported by Jauzac et al. (2015). Most
likely, the discontinuity was caused by a collision
Figure 15. LX–P and Y PSZ – diagrams. Clusters with only upper limits on the radio halo power are shown in teal-colored circles, while clusters with detected halos are
shown in dark red squares. On both diagrams, MACS J0416.1-2403 is represented with a star. In the Y PSZ – diagram, the orange star corresponds to the YSZ,500 value
reported by Planck Collaboration et al. (2015), while the blue star corresponds to the YSZ,500 value calculated from the gNFW fit to Bolocam presented in Czakon et al.
(2015). Error bars are drawn for all points, but some are very small and barely visible. Values for all clusters with the exception of MACS J0416.1-2403 are taken from
Cassano et al. (2013). Power-laws show the best-fitting L PX – and Y PSZ – correlations for radio halos with α > −1.5 (black) and for all known radio halos (including
ultra-steep spectrum halos; dark blue). Gray and light blue areas indicate the 95% confidence regions of the correlations. An interactive version of the diagrams is
available at http://hea-www.cfa.harvard.edu/~gogrean/Lx-P.html.
17
The Astrophysical Journal, 812:153 (19pp), 2015 October 20 Ogrean et al.
18. between the SW subcluster and S1, rather than by a
collision between the NE and SW subclusters.
4. The DM and gas components of the NE and SW
subclusters are well-aligned, which favors a scenario in
which the two subclusters are seen before first core
passage.
5. MACS J0416.1-2403 has a radio halo with a 1.4 GHz
power of 1.3 0.3 1024( ) W Hz−1
, which is some-
what less luminous than predicted by the L PX –
correlationfor radio halos without ultra-steep spectra.
However, the halo aligns well on the Y PSZ,500– correla-
tion, indicating that it is not underluminous for the cluster
mass.We could be observing the birth of a giant halo, or a
very rare ultra-steep halo.
We thank the referee for constructive comments. We also
thank Mathilde Jauzac for providing the coordinates of the
centers of the DM halos, and Becky Canning and Aurora
Simionescu for constructive discussions.
G.A.O. acknowledges support by NASA through a Hubble
Fellowship grant HST-HF2-51345.001-A awarded by the
Space Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy,
Incorporated, under NASA contract NAS5-26555. R.J.vW. is
supported by NASA through the Einstein Postdoctoral grant
number PF2-130104 awarded by the Chandra X-ray Center,
which is operated by the Smithsonian Astrophysical Observa-
tory for NASA, under contract NAS8-03060. A.Z. acknowl-
edges support by NASA through a Hubble Fellowship grant
HST-HF2-51334.001-A awarded by the Space Telescope
Science Institute, which is operated by the Association of
Universities for Research in Astronomy, Incorporated, under
NASA contract NAS5-26555. This research was performed
while T.M. held a National Research Council Research
Associateship Award at the Naval Research Laboratory
(NRL). Basic research in radio astronomy at NRL by T.M.
and T.E.C. is supported by 6.1 Base funding. F.A.S. acknowl-
edges support from Chandra grant G03-14131X.
The scientific results reported in this article are based on
observations made by the Chandra X-ray Observatory. Part of
the reported results are based on observations made with the
NASA/ESA Hubble Space Telescope, obtained from the Data
Archive at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555. The
HST observations are associated with program #13496. The
National Radio Astronomy Observatory is a facility of the
National Science Foundation operated under cooperative
agreement by Associated Universities, Inc. We thank the staff
of the GMRT that made these observations possible. The
GMRT is run by the National Centre for Radio Astrophysics of
the Tata Institute of Fundamental Research.
This research has made use of NASAʼs Astrophysics Data
System, and of the NASA/IPAC Extragalactic Database
(NED) which is operated by the Jet Propulsion Laboratory,
California Institute of Technology, under contract with the
National Aeronautics and Space Administration. Some of the
cosmological parameters in this paper were calculated using
Ned Wrightʼs cosmology calculator (Wright 2006). This
research made use of APLpy, an open-source plotting package
for Python hosted at http://aplpy.github.com.
Facilities: CXO (ACIS), HST (ACS).
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