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.
Merging galaxy clusters leave long-lasting signatures on the baryonic and non-baryonic cluster constituents,
including shock fronts, cold fronts, X-ray substructure, radio halos, and offsets between the dark matter (DM) and
the gas components. Using observations from Chandra, the Jansky Very Large Array, the Giant Metrewave Radio
Telescope, and the Hubble Space Telescope, we present a multiwavelength analysis of the merging Frontier Fields
cluster MACS J0416.1-2403 (z = 0.396), which consists of NE and SW subclusters whose cores are separated on
the sky by ∼250 kpc. We find that the NE subcluster has a compact core and hosts an X-ray cavity, yet it is not a
cool core. Approximately 450 kpc south–southwest of the SW subcluster, we detect a density discontinuity that
corresponds to a compression factor of ∼1.5. The discontinuity was most likely caused by the interaction of the
SW subcluster with a less massive structure detected in the lensing maps SW of the subclusterʼs center. For both
the NE and the SW subclusters, the DM and the gas components are well-aligned, suggesting that MACS J0416.1-
2403 is a pre-merging system. The cluster also hosts a radio halo, which is unusual for a pre-merging system. The
halo has a 1.4 GHz power of (1.3 ± 0.3) × 1024WHz−1, which is somewhat lower than expected based on the
X-ray luminosity of the cluster if the spectrum of the halo is not ultra-steep. We suggest that we are either
witnessing the birth of a radio halo, or have discovered a rare ultra-steep spectrum halo.
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.
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.
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.
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.
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.
Merging galaxy clusters leave long-lasting signatures on the baryonic and non-baryonic cluster constituents,
including shock fronts, cold fronts, X-ray substructure, radio halos, and offsets between the dark matter (DM) and
the gas components. Using observations from Chandra, the Jansky Very Large Array, the Giant Metrewave Radio
Telescope, and the Hubble Space Telescope, we present a multiwavelength analysis of the merging Frontier Fields
cluster MACS J0416.1-2403 (z = 0.396), which consists of NE and SW subclusters whose cores are separated on
the sky by ∼250 kpc. We find that the NE subcluster has a compact core and hosts an X-ray cavity, yet it is not a
cool core. Approximately 450 kpc south–southwest of the SW subcluster, we detect a density discontinuity that
corresponds to a compression factor of ∼1.5. The discontinuity was most likely caused by the interaction of the
SW subcluster with a less massive structure detected in the lensing maps SW of the subclusterʼs center. For both
the NE and the SW subclusters, the DM and the gas components are well-aligned, suggesting that MACS J0416.1-
2403 is a pre-merging system. The cluster also hosts a radio halo, which is unusual for a pre-merging system. The
halo has a 1.4 GHz power of (1.3 ± 0.3) × 1024WHz−1, which is somewhat lower than expected based on the
X-ray luminosity of the cluster if the spectrum of the halo is not ultra-steep. We suggest that we are either
witnessing the birth of a radio halo, or have discovered a rare ultra-steep spectrum halo.
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.
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.
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.
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.
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.
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.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
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
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.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
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.
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.
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.
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.
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.
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.
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.
Confirmation of the_ogle_planet_signature_and_its_characteristics_with_lens_s...Sérgio Sacani
O Telescópio Espacial Hubble e o Observatório W. M. Keck, no Havaí, fizeram confirmações independentes de um exoplaneta orbitando sua estrela central de uma distância bem grande. O planeta foi descoberto através de uma técnica chamada de microlente gravitacional.
Essa descoberta traz uma nova peça para o processo de caçada de exoplanetas: para descobrir planetas longe de suas estrelas, como Júpiter e Saturno estão do Sol. Os resultados obtidos pelo Hubble e pelo Keck apareceram em dois artigos da edição de 30 de Julho de 2015 do The Astrophysical Journal.
A grande maioria dos exoplanetas catalogados são aqueles localizados bem perto de suas estrelas, isso acontece porque as técnicas atuais de se caçar exoplanetas favorecem a descoberta de planetas com curtos períodos orbitais. Mas esse não é o caso da técnica de microlente gravitacional, que pode encontrar planetas mais frios e mais distantes com órbitas de longo período que outros métodos não são capazes de detectar.
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.
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.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
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
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.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
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.
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.
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.
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.
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.
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.
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.
Confirmation of the_ogle_planet_signature_and_its_characteristics_with_lens_s...Sérgio Sacani
O Telescópio Espacial Hubble e o Observatório W. M. Keck, no Havaí, fizeram confirmações independentes de um exoplaneta orbitando sua estrela central de uma distância bem grande. O planeta foi descoberto através de uma técnica chamada de microlente gravitacional.
Essa descoberta traz uma nova peça para o processo de caçada de exoplanetas: para descobrir planetas longe de suas estrelas, como Júpiter e Saturno estão do Sol. Os resultados obtidos pelo Hubble e pelo Keck apareceram em dois artigos da edição de 30 de Julho de 2015 do The Astrophysical Journal.
A grande maioria dos exoplanetas catalogados são aqueles localizados bem perto de suas estrelas, isso acontece porque as técnicas atuais de se caçar exoplanetas favorecem a descoberta de planetas com curtos períodos orbitais. Mas esse não é o caso da técnica de microlente gravitacional, que pode encontrar planetas mais frios e mais distantes com órbitas de longo período que outros métodos não são capazes de detectar.
Introduction to Searchmetrics - Presentation by Marcus Tober, Co-Founder & CEO of Searchmetrics at the NOAH 2013 Conference in London, Old Billingsgate on the 13th of November 2013.
Μαθήματικά E΄τάξης: Σχέδια μαθήματος GeogebraMartaki Fani
Τρία σχέδια μαθήματος που υλοποιήθηκαν με τη βοήθεια εφαρμογών που καταστευάστηκαν στο λογισμικό geogebra.
Το πρώτο αφορά την περίμετρο και το εμβαδόν και βασίστηκε σε μια δικιά μου εφαρμογή. Το δεύτερο αφορά στα πολλαπλάσια και τους διαρέτες και βασίστηκε σε έτοιμη εφαρμογή. Το τρίτο αφορά το Ε.Κ.Π. και βασίστηκε σε έτοιμη εφαρμογή.
Marie Montané - "L’influence du webdesign sur l’image de marque, ou dans quel...Geoffrey Dorne
Marie Montané - "L’influence du webdesign sur l’image de marque, ou dans quelle mesure le webdesign peut-il avoir un impact sur l’image de marque des agences web ?"
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.
O telescópio de rastreio VISTA do ESO encontrou uma horda de galáxias massivas anteriormente ocultas por poeira, que existiram quando o Universo era ainda bebê. Ao descobrir e estudar uma grande quantidade deste tipo de galáxias, os astrônomos descobriram, exatamente e pela primeira vez, quando é que tais monstros apareceram pela primeira vez no Universo.
O simples fato de contar o número de galáxias que existem em determinada área do céu permite aos astrônomos testar teorias de formação e evolução galática. No entanto, uma tarefa aparentemente tão fácil torna-se mais difícil quando tentamos contar galáxias cada vez mais distantes e tênues e é mais complicada ainda devido ao fato das galáxias mais brilhantes e fáceis de observar — as mais massivas no Universo — se tornarem mais raras à medida que os astrônomos observam o passado do Universo, enquanto que as galáxias menos brilhantes, mas muito mais numerosas, são ainda mais difíceis de detectar.
Uma equipe de astrônomos liderada por Karina Caputi do Instituto Astronômico Kapteyn da Universidade de Groningen, descobriu muitas galáxias distantes que não tinham sido detectadas anteriormente. A equipe utilizou imagens do rastreioUltraVISTA, um dos seis projetos que usam o VISTA para mapear o céu no infravermelho próximo, e fez um censo das galáxias tênues quando a idade do Universo estava compreendida entre 0,75 e 2,1 bilhões de anos.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
Chandra deep observation_of_xdcpj004402033_a_massive_galaxy_cluster_at_z_1_5Sérgio Sacani
Artigo apresenta os resultados obtidos pelo Chandra ao medir com precisão a massa do mais massivo aglomerado de galáxias do universo distante, o Aglomerado Gioiello.
The dispersion–brightness relation for fast radio bursts from a wide-field su...Sérgio Sacani
Despite considerable efforts over the past decade, only 34 fast radio
bursts—intense bursts of radio emission from beyond our Galaxy—
have been reported1,2
. Attempts to understand the population as a
whole have been hindered by the highly heterogeneous nature of the
searches, which have been conducted with telescopes of different
sensitivities, at a range of radio frequencies, and in environments
corrupted by different levels of radio-frequency interference
from human activity. Searches have been further complicated by
uncertain burst positions and brightnesses—a consequence of the
transient nature of the sources and the poor angular resolution of
the detecting instruments. The discovery of repeating bursts from
one source3
, and its subsequent localization4
to a dwarf galaxy at a
distance of 3.7 billion light years, confirmed that the population
of fast radio bursts is located at cosmological distances. However,
the nature of the emission remains elusive. Here we report a well
controlled, wide-field radio survey for these bursts. We found 20,
none of which repeated during follow-up observations between
185–1,097 hours after the initial detections. The sample includes
both the nearest and the most energetic bursts detected so far. The
survey demonstrates that there is a relationship between burst
dispersion and brightness and that the high-fluence bursts are
the nearby analogues of the more distant events found in highersensitivity,
narrower-field surveys5
.
Radio continum emission_of_35_edge_on_galaxies_observed_with_the_vlaSérgio Sacani
Usando um dos maiores rádio observatórios do mundo, o Very Large Array do National Radio Astronomy, um grupo de astrônomos descobriram que os halos ao redor dos discos das galáxias espirais são muito mais comuns do que se pensava anteriormente.
A equipe, dirigida pela Dra. Judith Irwin, da Universidade de Queens, em Kingston, ON, Canadá, observou 35 galáxias espirais próximas de lado, de 11 a 137 milhões de anos-luz de distância da Terra.
As galáxias espirais, como a nossa própria Via Láctea ou a famosa Galáxia de Andrômeda, possuem uma vasta maioria de suas estrelas, gás, e poeira num disco plano em rotação com braços espirais. A maior parte da luz e das ondas de rádio observadas com telescópios veem de objetos localizados nesse disco.
“Nós sabíamos antes que alguns halos existiam, mas, usando o poder total do VLA atualizado e o poder total de algumas técnicas de processamento de imagens, nós descobrimos que esses halos são muito mais comuns entre as galáxias espirais do que nós pensávamos antes”, explicou a Dra. Irwin.
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 Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Ga...Sérgio Sacani
We present Lyα imaging of 45 low-redshift star-forming galaxies observed with the Hubble Space Telescope. The
galaxies have been selected to have moderate to high star formation rates (SFRs) using far-ultraviolet (FUV)
luminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity. We employ a pixel stellar
continuum fitting code to obtain accurate continuum-subtracted Lyα, Hα, and Hβ maps. We find that Lyα is less
concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present
global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα
emission. We then show how the escape fraction of Lyα relates to a number of other measured quantities (mass,
metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly
anticorrelated with nebular and stellar extinction, weakly anticorrelated with stellar mass, but no conclusive
evidence for correlations with other quantities. We show that Lyα escape fractions are inconsistent with common
dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help
resolve the discrepancies. We present an SFR calibration based on Lyα luminosity, where the equivalent width of
Lyα is used to correct for nonunity escape fraction, and show that this relation provides a reasonably accurate SFR
estimate. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss
fractions at a given physical radius.
A candidate super-Earth planet orbiting near the snow line of Barnard’s starSérgio Sacani
Barnard’s star is a red dwarf, and has the largest proper motion
(apparent motion across the sky) of all known stars. At a distance
of 1.8 parsecs1
, it is the closest single star to the Sun; only the three
stars in the α Centauri system are closer. Barnard’s star is also
among the least magnetically active red dwarfs known2,3
and has
an estimated age older than the Solar System. Its properties make
it a prime target for planetary searches; various techniques with
different sensitivity limits have been used previously, including
radial-velocity imaging4–6
, astrometry7,8
and direct imaging9
, but all
ultimately led to negative or null results. Here we combine numerous
measurements from high-precision radial-velocity instruments,
revealing the presence of a low-amplitude periodic signal with a
period of 233 days. Independent photometric and spectroscopic
monitoring, as well as an analysis of instrumental systematic effects,
suggest that this signal is best explained as arising from a planetary
companion. The candidate planet around Barnard’s star is a cold
super-Earth, with a minimum mass of 3.2 times that of Earth,
orbiting near its snow line (the minimum distance from the star
at which volatile compounds could condense). The combination
of all radial-velocity datasets spanning 20 years of measurements
additionally reveals a long-term modulation that could arise from
a stellar magnetic-activity cycle or from a more distant planetary
object. Because of its proximity to the Sun, the candidate planet has a
maximum angular separation of 220 milliarcseconds from Barnard’s
star, making it an excellent target for direct imaging and astrometric
observations in the future.
The muse 3_d_view_of_the_hubble_deep_field_southSérgio Sacani
Artigo mostra como foram as observações feitas com o MUSE, o novo instrumento do VLT do campo profundo do Hubble. Além de descobrir 20 novos objetos, o MUSE conseguiu medir as propriedades das galáxias e até representar as mais próximas em 3 dimensões.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
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
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.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
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.
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
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Monitor common gases, weather parameters, particulates.
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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.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
2. MACSJ0717.5+3745 was discovered by Edge et al. (2003)
as part of the MAssive Cluster Survey (MACS; Ebeling
et al. 2001). It is an extremely massive, hot merging galaxy
cluster located at z = 0.5458, with a global temperature of
11.6±0.5 keV (Ebeling et al. 2007). A large-scale galaxy
filament that is connected to the cluster, with a projected length
of ∼4.5 Mpc, has also been reported (Ebeling et al. 2004;
Jauzac et al. 2012). The cluster is one of the most complex and
dynamically disturbed clusters known, with the merger
involving four separate substructures and shock-heated
∼20 keV gas (Ma et al. 2008, 2009; Limousin et al. 2012).
The large total mass of M M3.5 0.6 10vir
15( )
(Umetsu et al. 2014) and relatively shallow mass profile of
the cluster boosts the gravitational lens magnification and
results in a total lensed area that is about 3.5 arcmin2
for a
galaxy located at z 8. This area is higher than any other
known massive cluster (Zitrin et al. 2009a). For this reason, the
cluster is also part of the Cluster Lensing And Supernova
survey with Hubble (CLASH; Postman et al. 2012; Medezinski
et al. 2013) and the Hubble Space Telescope (HST) Frontier
Fields program.21
Since MACSJ0717.5+3745 is the largest known cosmic
lens, it is a prime target to search for radio and X-ray emission
associated with lensed background galaxies. In this work, we
present deep high-resolution JVLA observations which can be
used for this purpose. In addition, we carry out a search for
lensed X-ray sources with newly acquired deep Chandra data.
We adopt a ΛCDM cosmology with H 700 km s−1
Mpc−1
,
0.3m , and 0.7. With this cosmology, 1″ corresponds
to a physical scale of 6.387kpc at z=0.5458.
2. OBSERVATIONS AND DATA REDUCTION
2.1. JVLA Observations
JVLA observations of MACSJ07175+3745 were obtained
in the L-band (1–2 GHz) in the A-array configuration, in the
S-band (2–4 GHz) in the A- and B-array configurations, and in
the C-band (4.5–6.5 GHz) in the B-array configuration. All
observations were done using single 6hr runs, resulting in a
typical on-source time of ∼5hr. The total recorded bandwidth
was 1 GHz for the L-band, and 2 GHz for the S- and C-bands.
The primary calibrators were 3C138 and 3C147. The secondary
calibrator (J0713+4349) was observed for a couple of minutes
at 30–40minute intervals. All four circular polarization
products were recorded. An overview of the observations is
given in Table 1.
The data were reduced with CASA version 4.2.1 (McMullin
et al. 2007). The data from the different observing runs were all
reduced in the same way. For the two primary calibrators, we
used the clean-component models provided by CASA. We also
took the overall spectral index of the primary calibrator sources
into account, scaling the flux density for each channel.
As a first step, the data were Hanning smoothed and pre-
determined elevation-dependent gain tables and antenna
position offsets were applied. This was followed by automatic
flagging of radio frequency interference (RFI) using the tfcrop
mode of the CASA task flagdata. We then determined an
initial bandpass correction using 3C147. This bandpass was
applied and additional RFI was identified and flagged with the
AOFlagger (Offringa et al. 2010). The reason for applying
the bandpass is to avoid flagging good data due to the bandpass
roll off at the edges of the spectral windows.
Next, we determined complex gain solutions on 3C147 for
the central 10 channels of each spectral window to remove
possible time variations of the gains during the calibrator
observations. We pre-applied these solutions to find the delay
terms (gaintype = “K”) and bandpass calibration. Applying
the bandpass and delay solutions, we re-determined the
complex gain solutions for both primary calibrators using the
full bandwidth. We then determined the global cross-hand
delay solutions (gaintype = “KCROSS”) from the polarized
calibrator 3C138. For 3C138, we assumed a rotation measure
(RM) of 0radm−1
, and for the RL-phase difference we took
−15°. All relevant solutions tables were applied on the fly to
determine the complex gain solution for the secondary
calibrator J0713+4349 and to establish its flux density scale
accordingly. The absolute flux scale uncertainty due to
bootstrapping from the calibrators is assumed to be a few
percent (Perley & Butler 2013). As a next step, we used J0713
+4349 to find the channel-dependent polarization leakage
terms. 3C138 was used to perform the polarization angle
calibration for each channel.22
Finally, all solutions were
applied to the target field. The corrected data were then
averaged by a factor of 3 in time and a factor of 6 in frequency.
To refine the calibration for the target field, we performed
three rounds of phase-only self-calibration and a final round of
amplitude and phase self-calibration. For the imaging we
employed w-projection (Cornwell et al. 2008, 2005) to take the
non-coplanar nature of the array into account. Image sizes of up
to 122882
pixels were needed (A-array configuration) to
deconvolve a few bright sources outside the main lobe of the
primary beam. For each frequency band, the full bandwidth
was used to make a single deep Stokes I continuum image. We
used Briggs (1995) weighting with a robust factor of 0. The
spectral index was taken into account during the deconvolution
of each observing run (nterms = 3; Rau & Cornwell 2011).
We manually flagged some additional data during the self-
calibration process by visually inspecting the self-calibration
Table 1
JVLA Observations
L-band A-array S-band A-array S-band B-array C-band B-array
Observation dates 2013 Mar 28 2013 Feb 22 2013 Nov 5 2013 Sep 30
Frequencies coverage (GHz) 1–2 2–4 2–4 4.5–6.5
On source time (hr) ∼5 ∼5 ∼5 ∼5
Correlations full stokes full stokes full stokes full stokes
Channel width (MHz) 1 2 2 2
Integration time (s) 1 1 3 3
LAS (arcsec) 36 18 58 29
21
http://www.stsci.edu/hst/campaigns/frontier-fields/ 22
The polarization observations will be discussed in a forthcoming paper.
2
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
3. solutions. Clean masks were employed during the deconvolu-
tion. The clean masks were made with the PyBDSM source
detection package (Mohan & Rafferty 2015). The S-band
A-array and B-array configuration data were combined after the
self-calibration to make a single deep 2–4 GHz image. The final
images were made with Briggs weighting and a robust factor of
0.75, except for the C-band image, for which we employed
natural weighting. Images were corrected for the primary beam
attenuation, with the frequency dependence of the beam taken
into account. An overview of the resulting image properties,
such as rms noise and resolution, is given in Table 2.
2.2. Chandra Observations
MACSJ0717.5+3745 was observed with Chandra for a
total of 243 ks between 2001 and 2013. A summary of the
observations is presented in Table 3. The data sets were
reduced with CIAO v4.7 and CALDB v4.6.5, following the
same methodology that was described by Ogrean et al. (2015).
Point sources were detected with the CIAO script wavdetect
in the energy bands 0.5–2 and 2–7 keV, using wavelet scales of
1, 2, 4, 8, 16, and 32 pixels and ellipses with radii 5 around
the centers of the detected sources. Due to the complicated
morphology of MACSJ0717.5+3745, all sources found by
wavdetect were visually inspected and some false detections
associated with the extended ICM of the cluster were removed.
The local background around each point source was described
using an elliptical annulus with an inner radius equal to the
source radius and an outer radius approximately ∼3times
larger than the source radius. To model the X-ray spectra of the
point sources, the local background spectra were subtracted
from the corresponding source spectra. The spectra were
binned to a minimum of onecount/bin, and modeled with
XSPECv12.8.2 using the extended C-statistics23
(Cash 1979;
Wachter et al. 1979). All the source spectra were modeled as
powerlaws and included galactic absorption. The hydrogen
column density in the direction of MACSJ0717.5+3745 was
fixed to 8.4 1020 cm−2
, which is the sum of the weighted
average atomic hydrogen column density from the Leiden–
Argentine–Bonn (LAB; Kalberla et al. 2005) Survey and the
molecular hydrogen column density determined by Willingale
et al. (2013) from Swift data.
X-ray fluxes and luminosities were calculated in the energy
band 2–10 keV, with uncertainties quoted at the 90%
confidence level.
3. RESULTS
The 2–4 GHz S-band image of the cluster region is shown in
Figure 1. The most prominent source in the images is a large
filamentary radio relic that is associated with the cluster
MACSJ0717.5+3745. At the center of this relic, a narrow
angle tail (NAT) galaxy is visible, which is associated with a
cluster member at z=0.5528 (Ebeling et al. 2014). Another
tailed radio source (z=0.5399;Ebeling et al. 2014) is visible
at the far SE corner of the image. A bright linearly shaped FRI-
type radio source (Fanaroff & Riley 1974) is located to the SE.
This source is associated with an elliptical foreground galaxy
(2MASX J07173724+3744224) located at z=0.1546 (Bona-
fede et al. 2009). The radio relics and tailed radio galaxies
belonging to MACSJ0717.5+3745 will be discussed in a
separate paper (R. J. van Weeren et al. 2015, in preparation).
3.1. Source Detection
We used the PyBDSM24
source detection package to find and
determine the integrated flux densities of the radio sources in
the images. PyBDSM identifies “islands” of contiguous pixels
above a detection threshold and fits each island with Gaussians.
For detecting these islands, we took a threshold of 3 rms and a
pixel threshold of 4 rms, meaning that at least one pixel in each
island needs to exceed the local background by 4 rms. We
determined the local rms noise using a sliding box with a size of
300 pixels to take the noise increase by the primary beam
attenuation into account. We manually inspected the output
source catalogs and removed any source associated with the radio
relic and foreground FR-I source since these sources are larger
than the 300pixel box size for the local noise determination. The
source detection was run on all three frequency maps. The
locations of the detected sources are indicated on Figure 1.
We then searched for optical counterparts to the radio
sources within the area covered by the HST CLASH catalog
and HST Frontier Fields observations. For the detected radio
sources, we overlaid the radio contours on anHST Frontier
Fields color (v1.025
, F425W, F606W, and F814W band) image
to verify that the correct counterparts were identified;see
Figures 2 (lensed sources) and 5. Counterparts were found for
all radio sources. In a few cases, more than one optical
counterpart was identified for the radio source in the CLASH
catalog because of the complex morphology of the galaxy in
Table 2
Image Properties
L-band A-array S-band A+B-array C-band B-array
Resolution (arcsec×arcsec) 1.5×1.3 1.04×0.79 1.80×1.38
Noise (μJy beam−1
) 5.2 1.8 1.9
Table 3
Summary of the Chandra Observations
ObsID Instrument Mode Start Date Exposure Time (ks) Filtered Exposure Time (ks)
1655 ACIS-I FAINT 2001 Jan 29 19.87 17.06
4200 ACIS-I VFAINT 2004 Jan 10 59.04 58.02
16235 ACIS-I FAINT 2013 Dec 16 70.16 68.37
16305 ACIS-I VFAINT 2013 Dec 11 94.34 90.42
23
http://heasarc.gsfc.nasa.gov/docs/xanadu/xspec/wstat.ps
24
http://www.astron.nl/citt/pybdsm
25
https://archive.stsci.edu/pub/hlsp/frontier/macs0717/images/hst/
3
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
4. the HST images. An overview of all the compact lensed radio
sources that were found within the HST FOV is given in
Table 4. The properties of the sources that are not lensed, or for
which we could not determine if they were located behind the
cluster, are listed in Table 5.
To detect even fainter radio sources, we combined the
individual L-, S-, and C-band images into one deep 1–6.5 GHz
wideband continuum image, scaling with a spectral index26
(α)
of −0.5. This was done by convolving all maps to the
resolution of the C-band image. With the help of this deep
image, we identified about a dozen more sources below the
PyBDSM detection threshold in the individual maps, but with
peak fluxes above the local 3 rms. We manually determined the
flux densities of these sources in AIPS with the task JMFIT. In
addition, we visually identified five more sources in this deep
image that were below the 3 rms thresholds in the individual
maps and thus not recognized there. These sources are also
listed in Table 4 (and Table 5). We do not report integrated flux
densities for these sources since they are not clearly detected in
any of the individual maps. The CLASH photometric redshift
and best fitting BPZ (Benítez 2000) spectral template for each
source are also listed. For more details on the photometric
redshifts and spectral templates, the reader is referred to Molino
et al. (2014) and Jouvel et al. (2014). For 23 sources,
spectroscopic redshifts are available from Ebeling et al. (2014).
For the sources that are located at redshifts larger than the
cluster, we include the amplification factors in Table 4, taking
the average over all the eightpublicly available27
HST Frontier
Fields lensing models for MACSJ0717.5+3745. The ampli-
fications at a given redshift are calculated directly from the
mass (κ) and shear (γ) maps. For more details on how these
lensing models were derived, we refer to reader to the
references provided in Table 4. The reported uncertainties in
the amplification factors for the individual models are smaller
than the scatter between these models. Therefore, for the
uncertainty in the amplification factor, we take the standard
deviation between these models, which should better reflect the
actual uncertainties.
In total, we find 51 compact radio sources within the area
covered by the HST imaging. In this sample, 16 sources are
located behind the cluster, i.e., those where the 95% confidence
limit of the lower redshift bound places it beyond the cluster
redshift of z=0.5458. Of these sources, sevenhave amplifica-
tion factors larger than 2. We plot the location of the lensed radio
and X-ray sources on top of an amplification map for a z=2
source in Figure 3. We used the Zitrin-ltm-Gauss_v1
model amplification map as an example here. We discuss these
Figure 1. S-band B+A-array image made with robust = 0.75 weighting (Briggs 1995). The image has a resolution of 1 0 × 0 8 and a noise level of 1.8μJy beam−1
.
Compact radio and X-ray sources that fall within the HST coverage are indicated. Blue circles represent objects for which we could confirm that they are located
behind the cluster. Blue double circled sources have amplification factors 2 and are individually discussed in Section 3.2. Red circles represent cluster and
foreground radio sources. Light blue circled sources have too uncertain redshifts to determine if they are cluster members, foreground objects, or background objects.
Boxes indicate X-ray-detected sources, withcolor codingidentical to the radio sources. Black contours show the X-ray emission from Chandra smoothed with a
Gaussian with a FWHM of 10″. X-ray contours are drawn at levels of 5, 20, 50[ ] the background level (determined by measuring the background level around
2.5 Mpc, i.e., ;R200) from the cluster center. Both sky and instrumental background were included here.
26
F .
27
https://archive.stsci.edu/prepds/frontier/lensmodels/
4
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
5. lensed sources with amplification factors larger than 2 in some
more detail in Section 3.2. About a dozen radio sources are
associated with cluster members (i.e., z0.5 0.6phot ).
We also search for the presence of compact X-ray sources
within the HST FOV. In total, we detect sevenX-ray sources.
Five of these have radio counterparts. The X-ray sources are
also included in Table 4, with the measured X-ray fluxes. Two
of these X-ray sources which have radio counterpartsare
lensed by the cluster. The other X-ray sources are foreground
objects, cluster members, or have uncertain redshifts.
3.2. Lensed Sources
In this section, we discuss the radio and X-ray properties of
the lensed sources with amplification factors 2. These sources
are double circled in Figure 1. For the sources that are not
obvious AGNs(i.e., those that do not have X-ray counterparts),
we compute the star-formation rate based on the measured
radio luminosity. When converting from flux density to
luminosity, we used the amplification factors listed in Table 4.
The radio luminosity of the galaxies (non-AGN) can be
converted to mean star-formation rate over the past 10 years8
(Best et al. 2002) using
M
LSFR
yr
4.5
GHz
10 W Hz
, 11 22 1
( )⎜ ⎟
⎛
⎝
⎞
⎠
where Lν represents the k-corrected rest-frame radio luminosity
(which is also corrected for the amplification). The underlying
assumptions are that cosmic rays from SNe II trace star-
Figure 2. HST F435, F606W, and F814W postage stamp color images of the compact lensed radio sources in the MACSJ0717.3745 field. Similar postage stamp
images, but for sources that are not lensed, are shown in Figure 5. The red radio contours are from the 2–4 GHz S-band image and drawn at levels
1, 2, 4, 3 rms([ ]) , with 1.8rms μJy beam−1
. The beam size is indicated in the bottom left corner. We draw white radio contours for some images to aid
visibility (in case the area was not covered by all the HST filters). For sources without an S-band detection, we overlay contours from the C-band image (if detected
there) or the L-band image. We use contours from the combined L-, S-, and C-band images if the source is not detected in any of the three individual band images. The
values for rms for the L- and C-band images are listed in Table 2.
5
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
8. forming regions and that the number of SNe II is directly
proportional to the SFR. An advantage of these radio-derived
SFRs is that they are not significantly affected by dust
extinction. For our sources, we use the 3 GHz measurement
(unless stated otherwise), scaling with a spectral index of
0.5. The uncertainty in the radio-derived SFR is about a
factor of 2 (Bell 2003).
We can also compute the specific SFRs (sSFR) by
computing the stellar mass (M ) from the Spitzer 3.6 and
4.5 μm fluxes, following the approach by Rawle et al. (2014).
We corrected these fluxes for the amplification and computed
the K-correction using the BPZ spectral templates. The Spitzer
fluxes are taken from SEIP Source List (Enhanced Imaging
Products from the Spitzer Heritage Archive;we took the 3 8
diameter aperture flux densities). To compute the stellar mass,
we use the relation from Eskew et al. (2012)
M M S S D10 0.05 , 25.65
3.6 m
2.85
4.5 m
1.85
L
2[ ] ( ) ( )*
where Sλ is in units of Jy, and DL the luminosity distance in
megaparsecs. This relation was derived for the Large
Magellanic Cloud and assumes a Salpeter (1955) initial mass
function (IMF). It may break down for more strongly star-
forming systems and might also vary with metallicity. There-
fore, Equation (2) should be taken as an approximation to the
stellar mass.
3.2.1. Comments on Individual Sources
The source S0 has a spectroscopically measured redshift of
1.6852±0.001 (Ebeling et al. 2014) and an amplification
factor of 3.6±1.0 The source is associated with a disk galaxy
that has a central bright core in the HST image. The source is
also detected with Chandra (171 ± 25 net counts) with an
unabsorbed 2–10 keV flux of 1.71 100.20
0.16 14 erg s−1
cm−2
.
The photon index of the powerlaw of was determined at
0.89 0.42
0.33
. Together with the amplification factor and associated
uncertainty, this translates into a rest-frame luminosity of
0.29 100.07
0.11 44 erg s−1
, typical of an AGN. The optical
spectrum of the galaxy contains emission lines and the best
fitting BPZ template is that of an Sbc-type spiral galaxy.
Source S6 seems to be associated with a compact star-like
object. We also find an X-ray counterpart to the source
(150 ± 12 net counts). The object has a z 1.89phot 0.09
0.08
and an
amplification factor of 2.3±0.7. With this amplification
factor and redshift, the unabsorbed 2–10 keV flux of
8.48 101.08
1.24 15
erg s−1
cm−2
translates to a rest-frame
luminosity of 0.88 100.25
0.41 44
erg s−1
. The photon index of
the power law of was determined at 2.05 0.23
0.24
. The best fitting
BPZ template was that of a spiral galaxy, but the 2 value of
29.3 indicated a very poor fit. Given the star-like nature of the
object and poor fit, this source could be a quasar.28
S8 is located at z 1.15phot 0.03
0.04
and has a high amplification
factor of about 6.4±1.8. The best fitting BPZ template is that of
a starburst galaxy. Based on the S-band radio flux, we compute a
SFR of 15 7
12
M yr−1
. With M 2.4 101.0
1.4 10
* M we
compute a sSFR of 0.6 0.3
0.4
Gyr−1
. The errors take into account
the uncertainties in the radio and Spitzer flux density
measurements, amplification factor (Table 4), and redshift. For
the radio spectral index, we assumed an uncertainty of
0.3. Errors where estimated via a Monte Carlo approach,
drawing 104
realizations. Note that M*, SFR, and sSFR are
computed under the assumption that Equations (1) and (2) hold.
S9 is associated with a faint red galaxy with z 1.69phot 0.06
0.22
and is amplified with a factor of 3.4±1.0. The best fitting
BPZ template corresponds to a Sbc/ES0 galaxy. The source
has a relatively flat spectral index of 0.4 0.2 between
1.5 and 5.5 GHz. Based on the integrated flux density, we
compute a high SFR of 49 21
46
M yr−1
, scaling with 0.4.
A blue galaxy is located about 1″ to the east of this galaxy at
z 1.70photo 0.14
0.12
. With M 4.5 101.9
3.3 10
* M we compute
a sSFR of 1.1 0.5
0.8
Gyr−1
.
S45 is associated with a faint red galaxy with zphot
1.41 0.19
0.06
. It has a high amplification factor of 8.7±4.1 with a
best fitting spiral galaxy spectral template. We compute a SFR
of 17 11
29
M yr−1
.
In addition to the above sources that were detected in the
individual L-, S-, or C-band images, we also found two sources
in the deep broad-band stacked radio image with amplifications
2. S48 is associated with a red galaxy at z 0.91photo 0.06
0.07
,
with an amplification factor that is slightly less than 3. It is best
fit by a spiral BPZ template. S61 is associated with a blue
irregular galaxy. Its amplification factor is 3.4±2.5 and the
best fitting spectral template is that of a starburst galaxy. It is
listed as two separate objects in the CLASH photometric
catalog, with component 2 (Table 4) being a bright “knot” to
the north, embedded within the overall emission from the
galaxy (component 1). Thus, the HST images suggest that both
components belong the same galaxy with a complex morphol-
ogy. This is also consistent with the two photometric redshifts
that indicate z 1.6photo .
It should be acknowledged that some of the sources we
identify here, particularly those that lay behind the cluster
according to their photometric redshifts, may be multiple
Figure 3. Amplification/magnification map for a z=2 source from the
Zitrin-ltm-Gauss_v1 lensing model. For details of the lens modeling,
seeZitrin et al. (2009b). The location of the background compact sources are
indicated as in Figure 1. Black contours show the X-ray emission from
Chandra, smoothed with a Gaussian with a FWHM of 10″. X-ray contours are
drawn at levels of 5, 20, 50[ ] the X-ray background level as in Figure 1.
28
Note that the BPZ fitting did not include AGNs or quasar galaxy templates.
8
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
9. images of multiply lensed background sources. A brief search
according to the predictions of the model seen in Figure 3
neither assigned sources listed here to the same multiply
imaged sources, nor were other counter images located. We
also cross-checked the position of our lensed sources against
the list of multiply lensed sources by Limousin et al. (2012),
but none of our sources appear in this list. This means that—
adopting the lens model in hand—either the photometric
redshift for these images significantly deviate than those listed
in Table 4, or that the predicted counter images’s flux is below
the detection limit given a possibly smaller magnification, for
example. A more dedicated examination and search for
multiple images among our sample will be performed
elsewhere.
3.3. Radio Luminosity Function
It is expected that the number of star-forming galaxies
increases with redshift, peaking at z 2 (e.g., Madau &
Dickinson 2014). We compute the radio luminosity function
from the sources detected in our S-band image that have a
3 GHz flux density above 18μJy (10 rms). Above this flux
density, we should be reasonably completealso for sources that
are resolved.
For the luminosity function, we determine the volume
behind the cluster in which we could detect a hypothetical
source above the flux limit for a given luminosity. We then
divide the number of detected sources (for that luminosity
range) by the obtained volume. To compute the volume, we
take the varying magnification (as a function of position and
redshift) into account using the publicly available lensing
models and provided Python code.
We excluded the regions covered by the radio relic. We
scaled our 3 GHz S-band luminosities to 1.4 GHz taking
α = −0.5, to facilitate a comparison with the literature results
from Best et al. (2005). We limited ourselves to the range
z0.6 2.0, because we only detect a single source above
z 2. Restricting the redshift range also limits the effects of
the redshift evolution of the radio luminosity function.
The differences between the lensing models are larger than
the uncertainties provided for the individual models. We
therefore compute the volume for each for the eightmodels
listed in Table 4 and take the average. The same is done for
counting the number of sources in each luminosity bin (as this
also depends on the amplification factors). In Figure 4 we plot
the luminosity function averaged over these eightdifferent
lensing models. The red error bars represent the standard
deviation over the eightlensing models. The black error bars
show the combined uncertainty from the lensing models and
Poisson errors on the galaxy number counts. These two errors
were added in quadrature. We find that the uncertainties in the
redshifts and flux density measurements do not contribute
significantly to the error budget.
Another uncertainty for the derived luminosity function is
related to cosmic variance. Based on the computed volume, we
probe for the three luminosity bins and the number of objects in
each bin, we compute the cosmic variance using Trenti &
Stiavelli (2008). From this computation, we find that cosmic
variance introduces an extra uncertainty between 22% and
30%. Note, however, that this is a factor of a few smaller the
Poisson errors and scatter due to the different lensing models.
In Figure 4 we also plot the low-redshift (z 0.3)
luminosity function derived by Best et al. (2005). Although
the uncertainties in our luminosity function are substantial, we
find evidence for an increase in the number density of sources
of a factor between 4 and 10 compared to the Best et al. low-
redshift sample.
With a larger sample (for example, including all six Frontier
Fields clusters), it should become possible to map out the
luminosity function more accurately, as the Poisson errors can
be reduced by a factor of 6. Surveys covering a larger area
will be needed to map out the high-luminosity end. These
surveys can be shallower and do not require the extra
amplification by lensing. A major limitation of the precision
that can be achieved for the faintend of the luminosity
function, which can only be accessed with the power
of lensing, is the accuracy of the lensing models. This
highlights the importance of further improving the precision
of the Frontier Fields lensing models (see also Limousin
et al. 2015).
4. DISCUSSION AND CONCLUSIONS
In our JVLA radio images of MACSJ0717.5+3745, we
discovered sevenlensed sources with expected amplification
factors larger than 2. This makes MACSJ0717.5+3745 the
cluster with the largest number of known lensed radio sources.
Two of these radio sources are also detected in our Chandra
X-ray image. To our knowledge, only two other lensed X-ray
sources behind a galaxy cluster are known (Abell 370;Bautz
et al. 2000). All of the lensed sources (with amplification
factors 2) are located at z1 2 and most seem to be star-
forming galaxies with SFR of∼10–50 M yr−1
based on their
radio continuum fluxes. Our search for lensed radio sources is
different from previous radio studies performed by, e.g., Smail
et al. (1997), Garrett et al. (2005), Ivison et al. (2010a, 2010b),
and Berciano Alba et al. (2010), which targeted previously
known lensed submillimeter galaxies that have SFR ∼ 102
–
103
Me yr−1
. The two lensed sources that are also detected in
Figure 4. Radio luminosity function (number density of sources) at
z0.6 2.0 derived from our detected S-band sources. The luminosities
were scaled to 1.4 GHz and averaged over all eightlensing models. The
uncertainties in black are shown at1 and include the Poisson errors and scatter
between the eightdifferent lensing models. For reference, the red error bars
only show the scatter (standard deviation) in the luminosity function from the
eightdifferent lensing models. Results from Best et al. (2005) for a z 0.3
sample are also shown. The Best et al. sample is divided into SF galaxies
and AGNs.
9
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
10. our Chandra image have 2–10 keV X-ray luminosities of
∼1043–44
erg s−1
. We therefore classify these sources as AGNs
(e.g., Bauer et al. 2004).
From the derived luminosity function,we find evidence for
an increase in the number density of z0.6 2.0 radio
sources compared to the z 0.3 sample from Best et al.
Figure 5. HST F435, F606W, and F814W postage stamp color images around the compact radio sources in the MACSJ0717.3745 field. The sources in this panel are
cluster members, foreground objects, or sources with uncertain redshifts (so that we could not determine whether or notthey are lensed). Postage stamp images for the
lensed sources are shown in Figure 2. The red radio contours are from the 2–4 GHz S-band image and drawn at levels 1, 2, 4, 3 rms([ ]) , with
1.8rms μJy beam−1
. The beam size is indicated in the bottom left corner. We draw white radio contours for some images to aid visibility (in case the area was not
covered by all the HST filters). For sources without an S-band detection, we overlay contours from the C-band image (if detected there) or L-band image. We use
contours from the combined L-, S-, and C-band images if the source is not detected in any of the three individual band images. The values for rms for the L- and
C-band images are listed in Table 2. Note that for source S20 there is a very faint CLASH counterpart located precisely at the radio position.
10
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
11. (2005). The increase is expected given the cosmic evolution of
AGNs and SF galaxies between these two redshift ranges (e.g.,
Best et al. 2014; Madau & Dickinson 2014). Besides the
Poisson errors, we find that the scatter between the available
lensing models contributes significantly to the uncertainty in
our derived luminosity function.
From our JVLA observations, we conclude that, as expected,
lensing by massive (merging) clusters enables studying star-
forming galaxies at moderate to high redshifts, with the
advantage of not being affected by extinction. Some of these
radio sources have flux densities that are below the detection
limits of typical radio observations without the amplification by
lensing. In the case of MACSJ0717.5+3745, our highest
amplification factor is about9. To detect a source with a similar
signal-to-noise ratio in the S-band, without the lensing
amplification, would have required about 10 8 600 hr2
of JVLA integration time. Practically, this means that the
Square Kilometre Array (SKA) would be the only instrument
that could achieve such a detection without the help of lensing.
This example is similar to the lensed radio source found by
Jackson (2011). Radio observations also nicely complement
far-infrared and submillimeter observations that can detect
strongly star-forming galaxies behind clusters (e.g., Egami
et al. 2010; Rawle et al. 2015).
Besides the amplification of the integrated flux density, the
lensing magnification offers a chance to study these lensed
sources at high spatial resolution. In the case of MACSJ0717.5
+3745, all lensed radio sources are not or only slightly
resolved at the current 1 resolution. A larger sample of
lensing clusters is needed to increase the chances of finding a
rare brightand more highly magnified sourcethat would allow
a detailed spatially resolved study. Based on our
MACSJ0717.5+3745 result, for a massive lensing cluster
(for example, from the CLASH sample), we expect to detect
about a handful of lensed radio sources with a pointed ∼10hr
JVLA observation.
Figure 5. (Continued.)
11
The Astrophysical Journal, 817:98 (13pp), 2016 February 1 van Weeren et al.
12. Detection of background lensed X-ray sources suffer from
the increased X-ray background from the cluster’s ICM, in
particular in regions of high magnification (see Figure 3). This
makes X-ray observations of lensed sources comparatively less
efficient than optical or radio observations. In principle, by
choosing a harder energy band (i.e., 2–10 keV), the contrast
between a typical AGN and the ICM emission can be
increased. However, for massive lensing clusters, this does
not work so well because they are generally quite hot
(∼5–10 keV), producing significant ICM emission in the hard
X-ray band. In addition, the number density of X-ray sources
on the sky that could potentially be lensed by a cluster and
detected with current instruments with reasonable exposure
times is typically lower than that of radio observations and thus
decreases the chance of finding an object at high magnification
(e.g., Brunner et al. 2008; Condon et al. 2012). Extrapolating
from our MACSJ0717.5+3745 result, we expect to find of the
order of one lensed X-ray object (amplification 2) per
massive lensing cluster for a 102 ks Chandra observation.
Wethank the anonymous referee for useful comments. We
thank Megan Gralla for a discussion on the lensed radio
sources. The National Radio Astronomy Observatory is a
facility of the National Science Foundation operated under
cooperative agreement by Associated Universities, Inc. Support
for this work was provided by the National Aeronautics and
Space Administration through Chandra Award Number GO4-
15129X issued by the Chandra X-ray Observatory Center,
which is operated by the Smithsonian Astrophysical Observa-
tory for and on behalf of the National Aeronautics Space
Administration under contract NAS8-03060.
R.J.W. 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 Observatory for NASA under contract NAS8-
03060. 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. M.B.
acknowledges support by the research group FOR 1254 funded
by the Deutsche Forschungsgemeinschaft: “Magnetization of
interstellar and intergalactic media: the prospects of low-
frequency radio observations.” W.R.F., C.J., and F.A.-S.
acknowledge support from the Smithsonian Institution. F.A.-S.
acknowledges support from Chandra grant GO3-14131X. A.Z.
is supported by NASA through Hubble Fellowship grant HST-
HF2-51334.001-A awarded by STScI. This research was
performed while T.M. held a National Research Council
Research Associateship Award at the Naval Research Labora-
tory (NRL). Basic research in radio astronomy at NRL by T.M.
and T.E.C. is supported by 6.1 Base funding. M.D. acknowl-
edges the support of STScI grant 12065.007-A. P.E.J.N. was
partially supported by NASA contract NAS8-03060. E.R.
acknowledges a Visiting Scientist Fellowship of the Smithso-
nian Astrophysical Observatory, and the hospitality of the
Center for Astrophysics in Cambridge. Part of this work
performed under the auspices of the U.S. DOE by LLNL under
Contract DE-AC52-07NA27344.
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.
STScI is operated by the Association of Universities for
Research in Astronomy, Inc. under NASA contract NAS
5-26555. This work utilizes gravitational lensing models
produced by PIs Bradač Ebeling, Merten & Zitrin, Sharon,
and Williams funded as part of the HST Frontier Fields
program conducted by STScI. The lens models were obtained
from the Mikulski Archive for Space Telescopes (MAST). This
research has made use of the NASA/IPAC Infrared Science
Archive, which is operated by the Jet Propulsion Laboratory,
California Institute of Technology, under contract with the
National Aeronautics and Space Administration
Facilities: VLA, CXO, HST.
APPENDIX
COMPACT SOURCES:
CLUSTER AND FOREGROUND OBJECTS
In Table 5 we list the properties of all the radio and X-ray
sources that are cluster members, foreground objects, or
sources with uncertain redshifts (so that we could not determine
whether or notthey are lensed). We also provide HST color
postage stamp images around these radio sources in Figure 5.
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