The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
The massive relic galaxy NGC 1277 is dark matter deficient From dynamical mod...Sérgio Sacani
According to the Λ cold dark matter (ΛCDM) cosmology, present-day galaxies with stellar masses M? > 1011 M should contain
a sizable fraction of dark matter within their stellar body. Models indicate that in massive early-type galaxies (ETGs) with M? ≈
1.5 × 1011 M, dark matter should account for ∼15% of the dynamical mass within one effective radius (1 Re) and for ∼60% within
5 Re
. Most massive ETGs have been shaped through a two-phase process: the rapid growth of a compact core was followed by the
accretion of an extended envelope through mergers. The exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG population at z & 2. The best relic galaxy candidate discovered
to date is NGC 1277, in the Perseus cluster. We used deep integral field George and Cynthia Mitchel Spectrograph (GCMS) data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to 5 Re). By using Jeans anisotropic modelling, we find
a negligible dark matter fraction within 5 Re (fDM(5 Re) < 0.05; two-sigma confidence level), which is in tension with the ΛCDM
expectation. Since the lack of an extended envelope would reduce dynamical friction and prevent the accretion of an envelope, we
propose that NGC 1277 lost its dark matter very early or that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals, suggesting that some relic galaxies may result from dark matter stripping as they fell in and interacted
within galaxy clusters. Alternatively, NGC 1277 might have been born in a high-velocity collision of gas-rich proto-galactic fragments,
where dark matter left behind a disc of dissipative baryons. We speculate that the relative velocities of ≈2000 km s−1
required for the
latter process to happen were possible in the progenitors of the present-day rich galaxy clusters.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External ...Sérgio Sacani
Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a
host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore
sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending
on the dark matter composition, these gaps can provide unique constraints on dark matter models.
However, current samples are limited to the Milky Way. With its large field of view, deep imaging
sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and gaps significantly. This
paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other
nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream
and generate mock observations of these gaps with background stars in M31 and the foreground Milky
Way stellar fields. We assess Roman’s ability to detect gaps out to 10 Mpc through visual inspection
and with the gap-finding tool FindTheGap. We conclude that gaps of ≈ 1.5 kpc in streams that are
created from subhalos of masses ≥ 5×106 M⊙ are detectable within a 2–3 Mpc volume in exposures of
1000s–1 hour. This volume contains ≈ 150 galaxies, including ≈ 8 galaxies with luminosities > 109 L⊙.
Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap
characteristics in stellar streams and help constrain dark matter models.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
This document describes the discovery and characterization of an almost dark galaxy named Nube. Deep imaging with GTC revealed Nube has an extremely low surface brightness of 26.7 mag/arcsec^2 and a stellar mass of 4x10^8 solar masses. Follow-up observations with GBT detected HI emission from Nube, suggesting it is located 107 Mpc away. At this distance, Nube has a large half-mass radius of 6.9 kpc and low effective stellar density, making it the most extended low-surface brightness galaxy found. Its properties are difficult to reproduce in CDM simulations but are consistent with an ultra-light dark matter particle model.
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
The massive relic galaxy NGC 1277 is dark matter deficient From dynamical mod...Sérgio Sacani
According to the Λ cold dark matter (ΛCDM) cosmology, present-day galaxies with stellar masses M? > 1011 M should contain
a sizable fraction of dark matter within their stellar body. Models indicate that in massive early-type galaxies (ETGs) with M? ≈
1.5 × 1011 M, dark matter should account for ∼15% of the dynamical mass within one effective radius (1 Re) and for ∼60% within
5 Re
. Most massive ETGs have been shaped through a two-phase process: the rapid growth of a compact core was followed by the
accretion of an extended envelope through mergers. The exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG population at z & 2. The best relic galaxy candidate discovered
to date is NGC 1277, in the Perseus cluster. We used deep integral field George and Cynthia Mitchel Spectrograph (GCMS) data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to 5 Re). By using Jeans anisotropic modelling, we find
a negligible dark matter fraction within 5 Re (fDM(5 Re) < 0.05; two-sigma confidence level), which is in tension with the ΛCDM
expectation. Since the lack of an extended envelope would reduce dynamical friction and prevent the accretion of an envelope, we
propose that NGC 1277 lost its dark matter very early or that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals, suggesting that some relic galaxies may result from dark matter stripping as they fell in and interacted
within galaxy clusters. Alternatively, NGC 1277 might have been born in a high-velocity collision of gas-rich proto-galactic fragments,
where dark matter left behind a disc of dissipative baryons. We speculate that the relative velocities of ≈2000 km s−1
required for the
latter process to happen were possible in the progenitors of the present-day rich galaxy clusters.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External ...Sérgio Sacani
Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a
host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore
sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending
on the dark matter composition, these gaps can provide unique constraints on dark matter models.
However, current samples are limited to the Milky Way. With its large field of view, deep imaging
sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and gaps significantly. This
paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other
nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream
and generate mock observations of these gaps with background stars in M31 and the foreground Milky
Way stellar fields. We assess Roman’s ability to detect gaps out to 10 Mpc through visual inspection
and with the gap-finding tool FindTheGap. We conclude that gaps of ≈ 1.5 kpc in streams that are
created from subhalos of masses ≥ 5×106 M⊙ are detectable within a 2–3 Mpc volume in exposures of
1000s–1 hour. This volume contains ≈ 150 galaxies, including ≈ 8 galaxies with luminosities > 109 L⊙.
Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap
characteristics in stellar streams and help constrain dark matter models.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
This document describes the discovery and characterization of an almost dark galaxy named Nube. Deep imaging with GTC revealed Nube has an extremely low surface brightness of 26.7 mag/arcsec^2 and a stellar mass of 4x10^8 solar masses. Follow-up observations with GBT detected HI emission from Nube, suggesting it is located 107 Mpc away. At this distance, Nube has a large half-mass radius of 6.9 kpc and low effective stellar density, making it the most extended low-surface brightness galaxy found. Its properties are difficult to reproduce in CDM simulations but are consistent with an ultra-light dark matter particle model.
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
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.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
This document summarizes the results of a sub-mm survey of the Carina Nebula complex conducted with the LABOCA instrument on the APEX telescope. The survey mapped an area of 1.25° × 1.25° at 870 μm, revealing the morphology and distribution of cold dust clouds with masses down to a few solar masses. The total mass of clouds detected is estimated to be around 60,000 M☉. The cloud morphologies range from large clouds of several thousand solar masses to small diffuse clouds of only a few solar masses. The distribution of sub-mm emission generally agrees with Spitzer 8 μm maps, identifying clouds interacting with massive stars as well as infrared dark clouds. The survey provides crucial
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
The exceptional soft_x_ray_halo_of_the_galaxy_merger_ngc6240Sérgio Sacani
The document summarizes a recent 150-ks Chandra observation of the galaxy merger NGC 6240. Extended soft X-ray emission is detected over a 110x80 kpc region around NGC 6240. Spectral analysis finds the emission comes from hot gas with a temperature of around 7.5 million K and a total mass of about 10^10 solar masses. The gas properties suggest widespread star formation over the past 200 Myr rather than a recent nuclear starburst. The fate of the diffuse hot gas after the galaxy merger is uncertain but it may be retained and evolve into the halo of an elliptical galaxy.
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Obscuration beyond the nucleus: infrared quasars can be buried in extreme com...Sérgio Sacani
This document discusses how infrared quasars can be obscured by compact starbursts in their host galaxies in addition to the canonical dusty torus. The key points are:
1) Infrared quasars in starburst galaxies with star formation rates above 300 solar masses per year have a higher obscured fraction than at lower star formation rates, suggesting the host galaxy interstellar medium can significantly contribute to obscuring the quasar.
2) At star formation rates above 300 solar masses per year, submillimeter galaxies and infrared quasars have similarly compact submillimeter sizes of 0.5-3 kiloparsecs, indicating the dense interstellar medium in these compact starbursts can heavily obscure the quasar, even reaching
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
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.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
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.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
A three-dimensional map of the Milky Way using 66,000 Mira variable starsSérgio Sacani
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered
by the Optical Gravitational Lensing Experiment (OGLE) survey. The spatial distribution of the Mira
stars is analyzed with a model containing three barred components that include the X-shaped boxy
component in the Galactic center (GC), and an axisymmetric disk. We take into account the distance
uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is
R0 = 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the
Sun-GC line-of-sight is θ = 20.2
◦ ± 0.6
◦
(stat.) ± 0.7
◦
(sys.). We present, for the first time, a detailed
three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations.
Our analysis provides independent evidence for both the X-shaped bulge component and the flaring
disk (being plausibly warped). We provide the complete dataset of properties of Miras that were used
for calculations in this work. The table includes: mean brightness and amplitudes in nine photometric
bands (covering a range of wavelength from 0.5 to 12 µm), photometric chemical type, estimated
extinction, and calculated distance with its uncertainty for each Mira variable. The median distance
accuracy to a Mira star is at the level of 6.6%.
Detecting a disc bending wave in a barred-spiral galaxy at redshift 4.4Sérgio Sacani
The recent discovery of barred spiral galaxies in the early Universe (z > 2) poses questions of how these structures form and
how they influence galaxy evolution in the early Universe. In this study, we investigate the morphology and kinematics of the
far-infrared (FIR) continuum and [C II] emission in BRI1335-0417 at z ≈ 4.4 from ALMA observations. The variations in
position angle and ellipticity of the isophotes show the characteristic signature of a barred galaxy. The bar, 3.3+0.2 −0.2 kpc long in
radius and bridging the previously identified two-armed spiral, is evident in both [C II] and FIR images, driving the galaxy’s rapid
evolution by channelling gas towards the nucleus. Fourier analysis of the [C II] velocity field reveals an unambiguous kinematic
m = 2 mode with a line-of-sight velocity amplitude of up to ∼30–40 km s−1; a plausible explanation is the disc’s vertical bending
mode triggered by external perturbation, which presumably induced the high star formation rate and the bar/spiral structure. The
bar identified in [C II] and FIR images of the gas-rich disc galaxy ( 70 per cent of the total mass within radius R ≈ 2.2 disc
scale lengths) suggests a new perspective of early bar formation in high redshift gas-rich galaxies – a gravitationally unstable
gas-rich disc creating a star-forming gaseous bar, rather than a stellar bar emerging from a pre-existing stellar disc. This may
explain the prevalent bar-like structures seen in FIR images of high-redshift submillimeter galaxies.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
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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.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
This document summarizes the results of a sub-mm survey of the Carina Nebula complex conducted with the LABOCA instrument on the APEX telescope. The survey mapped an area of 1.25° × 1.25° at 870 μm, revealing the morphology and distribution of cold dust clouds with masses down to a few solar masses. The total mass of clouds detected is estimated to be around 60,000 M☉. The cloud morphologies range from large clouds of several thousand solar masses to small diffuse clouds of only a few solar masses. The distribution of sub-mm emission generally agrees with Spitzer 8 μm maps, identifying clouds interacting with massive stars as well as infrared dark clouds. The survey provides crucial
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
The exceptional soft_x_ray_halo_of_the_galaxy_merger_ngc6240Sérgio Sacani
The document summarizes a recent 150-ks Chandra observation of the galaxy merger NGC 6240. Extended soft X-ray emission is detected over a 110x80 kpc region around NGC 6240. Spectral analysis finds the emission comes from hot gas with a temperature of around 7.5 million K and a total mass of about 10^10 solar masses. The gas properties suggest widespread star formation over the past 200 Myr rather than a recent nuclear starburst. The fate of the diffuse hot gas after the galaxy merger is uncertain but it may be retained and evolve into the halo of an elliptical galaxy.
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Obscuration beyond the nucleus: infrared quasars can be buried in extreme com...Sérgio Sacani
This document discusses how infrared quasars can be obscured by compact starbursts in their host galaxies in addition to the canonical dusty torus. The key points are:
1) Infrared quasars in starburst galaxies with star formation rates above 300 solar masses per year have a higher obscured fraction than at lower star formation rates, suggesting the host galaxy interstellar medium can significantly contribute to obscuring the quasar.
2) At star formation rates above 300 solar masses per year, submillimeter galaxies and infrared quasars have similarly compact submillimeter sizes of 0.5-3 kiloparsecs, indicating the dense interstellar medium in these compact starbursts can heavily obscure the quasar, even reaching
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
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.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
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.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
A three-dimensional map of the Milky Way using 66,000 Mira variable starsSérgio Sacani
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered
by the Optical Gravitational Lensing Experiment (OGLE) survey. The spatial distribution of the Mira
stars is analyzed with a model containing three barred components that include the X-shaped boxy
component in the Galactic center (GC), and an axisymmetric disk. We take into account the distance
uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is
R0 = 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the
Sun-GC line-of-sight is θ = 20.2
◦ ± 0.6
◦
(stat.) ± 0.7
◦
(sys.). We present, for the first time, a detailed
three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations.
Our analysis provides independent evidence for both the X-shaped bulge component and the flaring
disk (being plausibly warped). We provide the complete dataset of properties of Miras that were used
for calculations in this work. The table includes: mean brightness and amplitudes in nine photometric
bands (covering a range of wavelength from 0.5 to 12 µm), photometric chemical type, estimated
extinction, and calculated distance with its uncertainty for each Mira variable. The median distance
accuracy to a Mira star is at the level of 6.6%.
Detecting a disc bending wave in a barred-spiral galaxy at redshift 4.4Sérgio Sacani
The recent discovery of barred spiral galaxies in the early Universe (z > 2) poses questions of how these structures form and
how they influence galaxy evolution in the early Universe. In this study, we investigate the morphology and kinematics of the
far-infrared (FIR) continuum and [C II] emission in BRI1335-0417 at z ≈ 4.4 from ALMA observations. The variations in
position angle and ellipticity of the isophotes show the characteristic signature of a barred galaxy. The bar, 3.3+0.2 −0.2 kpc long in
radius and bridging the previously identified two-armed spiral, is evident in both [C II] and FIR images, driving the galaxy’s rapid
evolution by channelling gas towards the nucleus. Fourier analysis of the [C II] velocity field reveals an unambiguous kinematic
m = 2 mode with a line-of-sight velocity amplitude of up to ∼30–40 km s−1; a plausible explanation is the disc’s vertical bending
mode triggered by external perturbation, which presumably induced the high star formation rate and the bar/spiral structure. The
bar identified in [C II] and FIR images of the gas-rich disc galaxy ( 70 per cent of the total mass within radius R ≈ 2.2 disc
scale lengths) suggests a new perspective of early bar formation in high redshift gas-rich galaxies – a gravitationally unstable
gas-rich disc creating a star-forming gaseous bar, rather than a stellar bar emerging from a pre-existing stellar disc. This may
explain the prevalent bar-like structures seen in FIR images of high-redshift submillimeter galaxies.
Ähnlich wie A giant thin stellar stream in the Coma Galaxy Cluster (20)
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
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.
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.
The technology uses reclaimed CO₂ as the dyeing medium in a closed loop process. When pressurized, CO₂ becomes supercritical (SC-CO₂). In this state CO₂ has a very high solvent power, allowing the dye to dissolve easily.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
(June 12, 2024) Webinar: Development of PET theranostics targeting the molecu...Scintica Instrumentation
Targeting Hsp90 and its pathogen Orthologs with Tethered Inhibitors as a Diagnostic and Therapeutic Strategy for cancer and infectious diseases with Dr. Timothy Haystead.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
Mending Clothing to Support Sustainable Fashion_CIMaR 2024.pdfSelcen Ozturkcan
Ozturkcan, S., Berndt, A., & Angelakis, A. (2024). Mending clothing to support sustainable fashion. Presented at the 31st Annual Conference by the Consortium for International Marketing Research (CIMaR), 10-13 Jun 2024, University of Gävle, Sweden.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
A giant thin stellar stream in the Coma Galaxy Cluster
1. A&A 679, A157 (2023)
https://doi.org/10.1051/0004-6361/202346780
c The Authors 2023
Astronomy
&
Astrophysics
A giant thin stellar stream in the Coma Galaxy Cluster
Javier Román1,2,3 , Robert Michael Rich4, Niusha Ahvazi5,6 , Laura V. Sales5 , Chester Li4,7, Giulia Golini2,3 ,
Ignacio Trujillo2,3 , Johan H. Knapen2,3, Reynier F. Peletier1 , and Pablo M. Sánchez-Alarcón2,3
1
Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
e-mail: jromanastro@gmail.com
2
Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
3
Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
4
Department of Physics & Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095-1547, USA
5
Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA
6
Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA
7
Department of Astronomy, University of Washington, 3910 15th Avenue, NE, Seattle, WA 98195, USA
Received 30 April 2023 / Accepted 13 October 2023
ABSTRACT
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
Key words. galaxies: clusters: individual: Coma – galaxies: evolution – galaxies: interactions – galaxies: photometry
1. Introduction
Extremely low-surface-brightness features in the form of stel-
lar streams and haloes provide crucial information for under-
standing the hierarchical model of galaxy evolution in a Λ-CDM
framework (Bullock & Johnston 2005; Johnston et al. 2008;
Cooper et al. 2010; Pillepich et al. 2014; Monachesi et al. 2019;
Rey & Starkenburg 2022; Genina et al. 2023). These structures
are created from the continuous accretion of satellites, and rep-
resentative examples are found in the environments of the Local
Group (e.g., Belokurov et al. 2006; McConnachie et al. 2018;
Ibata et al. 2021; Dodd et al. 2023) and of nearby galaxies (e.g.,
Mouhcine et al. 2010; Crnojević et al. 2016) by counting indi-
vidual stars.
The availability of high-precision stellar positions and veloc-
ities – mainly in the Milky Way environment – has promoted
intense research in this field (see a review by Helmi 2020).
One of the applications of the study of stellar streams, given
their extremely low stellar density, is their ability to reveal the
gravitational potential in which they reside (e.g., Johnston et al.
1999; Dubinski et al. 1999; Sanders & Binney 2013; Reino et al.
2021; Pearson et al. 2022), especially for the case of cold stellar
streams (Bonaca & Hogg 2018). Because of their coherent stel-
lar motion, any nearby perturbation by a conspicuous low-mass
potential can be identified in parameter space (e.g., Ibata et al.
2002; Carlberg 2012; Erkal & Belokurov 2015). This is par-
ticularly interesting for the case of a potential perturbation by
dark matter subhaloes, which could provide relevant information
about the properties of dark matter in already known streams
in the Milky Way such as Pal 5 or GD-1 (Erkal et al. 2016;
Banik & Bovy 2019; Ibata et al. 2020; Banik et al. 2021).
Because of the large amount of information contained in
stellar streams, there have been sustained efforts to explore
these structures in external galaxies in order to obtain a
larger environmental and statistical context (Tal et al. 2009;
Martínez-Delgado et al. 2010; Rich et al. 2012; Duc et al. 2015;
Trujillo et al. 2021; Martínez-Delgado et al. 2023a). However,
resolving individual stars is only feasible out to a few mega-
parsecs, and the significant observational challenges of large-
area, low-surface-brightness photometry (Knapen & Trujillo
2017; Mihos 2019) mean that the very low-surface-brightness
regimes at which cold stellar streams have been identified in
the Milky Way are mostly unexplored at greater distances, and
most of the expected faint stellar streams remain undetected
(Martin et al. 2022).
With the imminent arrival of the new generation of
instrumentation and deep optical surveys such as Euclid
(Euclid Collaboration 2022a), the Rubin Observatory (Ivezić
et al. 2019), and the Nancy Grace Roman Space Telescope
(Akeson et al. 2019), along with significant technical efforts
(Euclid Collaboration 2022b; Smirnov et al. 2023; Kelvin et al.
2023), it is expected that the attainable surface-brightness lim-
its will increase the number of stellar streams detected in exter-
nal galaxies by orders of magnitude (Pearson et al. 2019). This
will provide a broader environmental context and a greater
understanding of the processes involved, yielding invaluable
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A157, page 1 of 14
2. Román, J., et al.: A&A 679, A157 (2023)
information in both galactic evolution models and near-field
cosmology.
We present the first results of an extensive observational
campaign to explore the Coma cluster at the ultralow-surface-
brightness regime: the HERON Coma Cluster Project. The Coma
cluster is one of the most-studied extragalactic objects, and is
of particular historical significance (see a historical review by
Biviano 1998), for example being the site of the discovery of
first evidence of dark matter (Zwicky 1933) or intracluster-
light (Zwicky 1951). The existence of galactic debris in Coma
(Trentham & Mobasher 1998; Gregg & West 1998) and other
clusters (Conselice & Gallagher 1999; Calcáneo-Roldán et al.
2000; Mihos et al. 2017) is direct evidence of the processes
of galactic cannibalism and accretion giving rise to the build-
ing of the intragroup and intracluster light haloes (Rudick et al.
2009; DeMaio et al. 2015; Montes 2022). As Coma is one of the
most massive local clusters with intense merger activity (e.g.,
Jiménez-Teja et al. 2019; Gu et al. 2020), it is an ideal setting
for carrying out an exploration of this type of structure, pro-
viding crucial information on the environmental and interaction
processes taking place in clusters.
Here, we report the discovery of the Giant Coma Stream,
an extremely faint, thin, and free-floating stellar stream in the
outskirts of the Coma galaxy cluster. At 510 kpc in length, it
is several times longer than the two previously identified stel-
lar streams in the Coma cluster (Trentham & Mobasher 1998;
Gregg & West 1998) or other clusters (Conselice & Gallagher
1999; Calcáneo-Roldán et al. 2000; Mihos et al. 2017), while
showing orders-of-magnitude lower surface brightness and total
mass. We show that this new stream is consistent with features
found in numerical simulations of hierarchical cluster formation
(Illustris TNG). We assume a distance of 100 Mpc for Coma
(Liu & Graham 2001), corresponding to a distance modulus of
m− M = 35.0 mag and a spatial scale of 0.462 kpc arcsec−1
using
cosmological parameters from Planck Collaboration VI (2020).
We use the AB photometric system throughout this work.
2. Observations and detection
2.1. HERON data
We carried out an extensive observational campaign of deep
observations in the Coma Cluster in g and r bands with the 0.7 m
Jeanne Rich Telescope. This telescope is mainly dedicated to the
Halos and Environments of Nearby Galaxies (HERON) Survey
(Rich et al. 2019), and is designed to be particularly efficient in
the low-surface-brightness regime. It has a single Finger Lakes
Instruments ML09000 detector with 30482
12 µm pixels with a
scale of 1.114 arcsec pix−1
, allowing a 57 × 57 arcmin field of
view. A thorough technical description of the instrumentation is
provided by Rich et al. (2017). Observations in this work are part
of the HERON Coma Cluster Project (Román et al., in prep.),
the goal of which is to carry out a study of the diffuse light of the
Coma cluster to unprecedented limits in surface brightness.
Observations were conducted in the spring and summer of
2019 for the g band and 2020 for the r band. A total of 461
and 579 exposures of 300 s were taken in the g and r bands,
respectively. Observational conditions were mostly dark. Dither-
ing steps of tens of arcminutes were performed with the aim of
covering an area of 1.5×1.5◦
centered on Coma. The data reduc-
tion was performed by standard subtraction of combined super-
bias and superdarks for each night from the science images. Flat
fields were constructed by combining and normalizing the heav-
ily masked bias-subtracted and dark-subtracted science images.
Astrometry was performed on all images individually with
the Astrometry.net software package (Lang et al. 2010) and
SCAMP (Bertin 2006). The images were then reprojected onto
a common astrometrical grid with SWARP (Bertin et al. 2002)
and photometrically calibrated with the Dark Energy Camera
Legacy Survey (DECaLS; Dey et al. 2019) as a reference. The
images were combined with a very conservative sky fitting based
on Zernike polynomials to preserve the information at low sur-
face brightness. We used orders between 1 and 4 depending on
the degree of gradients in the images, always using the low-
est possible order able to fit the gradients of each individual
image.
The total exposure time was 38.4 h and 48.25 h in the g and
r bands, respectively. The maximum surface brightness limits
in these data are 30.1 and 29.8 mag arcsec−2
[3σ, 1000
× 1000
]
in both g and r bands (see definition by Román et al. 2020). In
the region of interest here, the surface brightness limits reach
29.5 mag arcsec−2
[3σ, 1000
×1000
] in both g and r bands. The see-
ing conditions were not restrictive as we were interested in the
diffuse light, producing a final seeing of approximately 3 arcsec
in both g and r bands. Further details about this project and data
will be provided in an upcoming publication.
A preliminary visual analysis of these data allowed us to
identify an extremely faint feature with very thin morphology
(see Fig. 1a). Its detected length and width are approximately
18.5 and 1 arcmin, respectively.
2.2. WHT data
To obtain confirmation of this feature, we carried out follow-
up observations with the 4.2 m William Herschel Telescope. We
used the PF-QHY Camera with a field of view of 7.10
× 10.70
and pixel scale of 0.2667 arcsec pix−1
. We used an L luminance
filter, which is a UV-IR blocker with a high efficiency of 95% in
the range of 370−720 nm, thus covering the g and r SDSS filters.
The purpose of using a wide luminance band is to achieve maxi-
mum detection power given the extremely low surface brightness
of this feature. A total of 200 individual 180 s exposures were
obtained on June 4, 6, 11, and 14, 2021, under seeing conditions
of approximately 1.2 arcsec. The data processing was similar to
that used for the HERON data. Throughout the observations,
we carried out extensive dithering, with maximum separation of
about 5 arcmin (half of the field of view) in order to obtain high
efficiency in the low-surface-brightness regime, minimizing the
presence of gradients and allowing us to build a flat field with
the science images.
Due to the extensive dithering of the observations, the expo-
sure time varies with position. In Fig. A.1 we show the exposure
time and equivalent depth along the footprint of the observations.
In the maximum exposure region of 10 h, the limiting surface
brightness reaches 31.4 mag arcsec−2
[3σ, 1000
× 1000
] in the L
luminance band. A relatively large portion of about 6 × 8 arcmin
of the area of the image, including the central region of the
stream, has a surface brightness limit of 31.0 mag arcsec−2
[3σ,
1000
×1000
]. The resolution is 1.2 arcsec in full width at half max-
imum (FWHM).
The WHT luminance band image confirms the existence
of the narrow feature identified in the HERON data, achiev-
ing deeper surface brightness limits and higher resolution (see
Figs. 1b and c) over the central region (14 × 17 arcmin) of the
stream. We searched visually for potential remnants or overden-
sity from a parent galaxy. However, the stream appears com-
pletely featureless, especially in the higher resolution and deeper
WHT image that samples the central region.
A157, page 2 of 14
3. Román, J., et al.: A&A 679, A157 (2023)
Fig. 1. General view of the Giant Coma Stream and its location in the Coma Cluster. Bottom: Color composite HERON image in the g and r bands.
The dark background is constructed with the sum image. Uper right: WHT image of the Giant Coma Stream in L luminance (dark background) on
a color image using g and r bands from the DECaLS survey. Upper left: Zoom onto the central region of the WHT image.
3. Association with the Coma Cluster
The detection of this stream in three images with two different
telescopes allows us to confirm its discovery and to rule out a
possible residual flux due to instrumentation or data processing.
The presence of globular clusters usually traces the trajec-
tories of streams (Mackey et al. 2019), and can also provide an
estimate of their distance through measurement of the peak of
the globular cluster luminosity function (Rejkuba 2012). How-
ever, the HERON data do not have enough point-source depth,
and do not allow color filtering with only the g and r bands.
There are no HST data available over the area, and the only
multi-band data available from DECaLS have insufficient point
source depth, making detection of globular clusters infeasible
A157, page 3 of 14
4. Román, J., et al.: A&A 679, A157 (2023)
until better data are obtained. In this section, we present an anal-
ysis performed to ensure that the detected feature is indeed a
stellar stream located in Coma.
3.1. Potential resolved stars
We explore the possibility of the existence of an overdensity of
point-like sources over the stream region, which would indicate
a close distance. For this, we use SExtractor (Bertin 2006)
with a detection threshold of 1σ. We do not apply any magnitude
criteria other than selecting sources compatible with point-like
sources, and for this we select sources with a stellarity index of
higher than 0.5.
The middle panel of Fig. 2 shows the density of point-like
sources that we can associate with low-luminosity stars. Inter-
estingly, this stream is not resolved into stars in the WHT data,
appearing as an extremely smooth and low-surface-brightness
feature. Considering that this feature is not resolved into stars,
we follow the analysis by Zackrisson et al. (2012) to impose a
lower limit on distance. The fact that stars are unresolved in our
highest-resolution data with a seeing of 1.2 arcsec and a surface
brightness of approximately 29 mag arcsec−2
(detailed in later
sections) suggests that the feature must be at a distance of at
least 1 Mpc.
3.2. Far-infrared counterpart
In order to explore the possibility that the stream could be a
trace of dust from the interstellar medium (ISM) or Galactic
cirrus of the Milky Way, we used data available from the Her-
schel space telescope at 250 µm (Pilbratt et al. 2010). Due to
its low temperature, Galactic cirrus are efficiently detected in
far-infrared (FIR) and submillimeter bands (Low et al. 1984;
Veneziani et al. 2010). The Herschel data at 250 µm offer a sig-
nificant advantage over data from other instruments, such as
IRAS (Neugebauer et al. 1984) or the Planck observatory with
its 857 GHz band (Planck Collaboration XXIV 2011), both in
detection power and – importantly for our case – resolution.
The lower panel of Fig. 2 shows a comparison between our
optical data and the Herschel 250 µm band of the same field. The
images have been stretched in the optical to provide maximum
contrast for the detection of the faintest sources. The FWHM
of the 250 µm Herschel data is 17.6 arcsec, which is lower than
the detected stream width in optical bands of 1 arcmin. Visually,
there is no emission trace in the 250 µm band, either in the region
where the stream is located or adjacent to it. The only detectable
emission in 250 µm is that corresponding to galaxies along the
line of sight, among which we can highlight the strong emission
from the late-type galaxy NGC 4848.
In order to quantify the 250 µm emission over the region of
the stream, we calculated the total flux in the aperture defined
by the dashed lines shown in Fig. 2 and outside this region. This
aperture is defined using HERON optical data, and is detailed in
Sect. 4.1. This is done on the heavily masked image, avoiding
the integration of regions corresponding to external sources that
appear in the image. The average sky background value over the
region of the stream is Sν,250 µm = −0.02 ± 0.04 MJy sr−1
and that
outside this region is Sν,250 µm = 0.02 ± 0.01 MJy sr−1
. Therefore,
the stream has no emission in the 250 µm band, at least up to the
value defined by the sky background noise of these data.
The absence of a 250 µm counterpart to the optically detected
stream suggests that the Galactic cirrus emission is an unlikely
Fig. 2. Comparison between optical point-like source density and far-
IR emission in the central region (13.5 × 7.6 arcmin). Top panel: WHT
image in the luminance L filter color coded in surface brightness accord-
ing to the upper color bar. Middle panel: density of detected point-like
sources in the region with WHT data. Lower panel: 250 µm counter-
part with the Herschel space telescope. The image is color coded in
Sν according to the lower color bar. The dashed lines mark elliptical
surface brightness contours of approximately µL = 26 mag arcsec−2
for
the galaxies named in the top panel, and µL = 29.5 mag arcsec−2
for the
location of the Giant Coma Stream.
explanation for the origin of the feature. Additional reasons to
rule out a Galactic cirrus contamination are that this celestial
region is very close to the Galactic pole (b = 88◦
), with a low
extinction by dust (Ar = 0.02 mag; Schlafly & Finkbeiner 2011)
and that the stream is almost one dimensional, not showing the
A157, page 4 of 14
5. Román, J., et al.: A&A 679, A157 (2023)
Fig. 3. Graphical representation of galactic associations in the line of sight of the Giant Coma Stream. Groups and clusters of local galaxies
(Vrad < 3500 km s−1
) and their apparent virial radii are represented with gray circles. Galaxies with redshift in the range of 3500 km s−1
< Vrad <
10 000 km s−1
are represented with black dots. The apparent Coma virial radius is represented with a red circle. The position and longitude of the
Giant Coma Stream is represented with a red segment.
expected fractal morphology of cirrus in optical wavelengths
(Marchuk et al. 2021).
3.3. Environmental analysis
The extremely low surface brightness of this feature makes
it highly challenging to obtain spectroscopic information with
which to measure its redshift. We have not found any gas detec-
tions in the region using the NASA/IPAC Extragalactic Database,
nor counterparts in recent work by Bonafede et al. (2022).
Assuming that the feature is indeed a stellar stream, its elon-
gated morphology suggests that it must be a tidal feature and
therefore should be associated with some structure that impacts
it gravitationally. Considering its large apparent size, beyond the
obvious possible association with the adjacent Coma cluster, we
explored a potential association with some nearby structures in
close projection.
Figure 3 shows a celestial coordinate map with large-
scale structures in the line of sight of the stream. We make
use of the catalogue of nearby groups within 3500 km s−1
by
Kourkchi & Tully (2017) to identify these structures. Kourkchi
& Tully (2017) also offer estimates of the virial radius of these
structures.
We plot all groups together with their virial radii in Fig. 3.
We convert from physical to projected coordinates using the
same cosmological parameters as those in Kourkchi & Tully
(2017) with H0 = 75 km s−1
Mpc−1
. Where a distance is not avail-
able for a group, we use a direct conversion by Hubble’s law
using the radial velocity. We find that only sparse groups do
not have measured distances, and in any case, they are not close
in projection to the Coma Cluster. As a complement, and given
that the Kourkchi & Tully (2017) catalogue only contains groups
up to 3500 km s−1
, we plot galaxies with radial velocities of
between 3500 and 10 000 km s−1
obtained from the NASA/IPAC
Extragalactic Database as black points. This upper limit is used
because it is the maximum radial velocity of the galaxies con-
tained in the central region of the Coma cluster. To represent the
virial radius of the Coma cluster, we rely on Ho et al. (2022),
A157, page 5 of 14
6. Román, J., et al.: A&A 679, A157 (2023)
giving 2.4 Mpc with H0 = 75 km s−1
Mpc−1
. We also plot the
length and location of the stream as a red segment.
We can comment on some nearby structures. First, the Virgo
Galaxy Cluster, which could be a potential host for the stream,
is located at approximately 13◦
projected separation from Coma.
With a calculated virial radius of 1.3 Mpc for the Virgo Cluster,
this corresponds to an apparent size of 4.4◦
. The stream would
therefore be located at a projected distance of 3.9 times the virial
radius of the Virgo Cluster. The M 94 group is the other struc-
ture with a large apparent size, having a virial radius of 365 kpc,
which is equivalent to 4.4◦
. The stream is located at three times
the virial radius of the M 94 Group. NGC 4725, located at a dis-
tance of 12 Mpc, has a virial radius of 143 kpc, equivalent to
0.63◦
, with the stream at 5.1 times its virial radius. Next, the
group of NGC 4565, located at a distance of 13 Mpc, has a virial
radius of 343 kpc, equivalent to 1.4◦
, leaving the stream at more
than 4.4 times its virial radius. Finally, the closest structure in
terms of virial radius is M 64, located at a distance of 5 Mpc,
with a virial radius of 224 kpc, equivalent to 2.34◦
. The stream
would therefore be projected at a distance of 2.8 times this virial
radius.
We explored the possibility that the stream could be caused
by a disturbance from a galaxy that overlaps with it in the line of
sight. In Fig. 2 the most prominent candidates are identified by
name. In particular, the pair of overlapping galaxies UGC 08071
and LEDA 083688 could be candidates to produce the stream.
However, our very deep images do not show any sign of asym-
metry in them. Furthermore, the radial velocities of UGC 08071
and LEDA 083688 are 6933 ± 2 km s−1
and 8169 ± 2 km s−1
,
respectively, and these objects are therefore located more than
1200 km s−1
apart in velocity space (the radial velocity of galax-
ies in Coma ranges from 4000 to 10 000 km s−1
). This makes it
highly unlikely that they could have interacted at such a high
velocity while leaving no asymmetry in the time during which
the stream expanded. The other galaxies in the line of sight also
show no appreciable asymmetry that would be compatible with
the occurrence of the stream. We note that for a tidal-force cal-
culation between galaxies in the line of sight, a distance value
between them is necessary. However, in this case, a relative dis-
tance value is not easily obtained, considering that we are in a
clustered environment, and that very close projections between
galaxies might only be apparent. This would mean that galaxies
in close projection could be separated by tens or even hundreds
of kiloparsecs. We therefore consider the potential presence of
disturbance in the outer parts of galaxy haloes to form the basis
of the most reliable approach to identifying the presence of inter-
action between galaxies.
We further investigate a possible counterpart to a radio relic.
Radio relics are diffuse structures detected in radio by syn-
chrotron emission frequently found in interacting galaxy clusters
(see a review by van Weeren et al. 2019). Notably, these radio
relics are often found in the peripheral regions of galaxy clusters,
with morphologies similar to those of the stream (Feretti et al.
2012; Jee et al. 2015). Although no optical counterpart has been
found for these radio relics by previous works, due to the
extreme surface brightnesses that we explore in this work, it is
interesting to look for a counterpart to a radio relic. However, we
do not identify a counterpart in the deepest and most recent data
in Coma by Bonafede et al. (2022).
From this analysis, we conclude that the stream is embed-
ded within the region of influence or virial radius of the Coma
Galaxy Cluster, and does not overlap with the virial radius of
any other structure in the line of sight. No other galactic associa-
tion, such as a group or cluster, overlaps with the location of the
stream, and there is no galaxy in the line of sight that could be the
origin of the stream. This indicates that the stream is most likely
associated with Coma and that there is no other particular galaxy
or galactic association that can explain its clearly disturbed
morphology.
4. Analysis
4.1. Photometry
To better constrain the nature and possible origin of the stream,
we performed a photometric analysis of the Giant Coma Stream
with the two different datasets available to us. The HERON
image provides two photometric bands g and r with surface
brightness limits of 29.5 mag arcsec−2
[3σ, 1000
× 1000
] in g and
r bands, respectively, in the region of interest, with a spatial reso-
lution of ≈3 arcsec FWHM and completely covering the region.
The WHT data partially cover the central region of the stream
with an average depth of 31.0 mag arcsec−2
[3σ, 1000
× 1000
] in
the luminance band and a spatial resolution of approximately
1.2 arcsec in FWHM. Given the different characteristics of the
two datasets, we performed a different analysis on each, focus-
ing on obtaining different photometric properties.
We first analyzed the photometry using the HERON data.
In the top panel of Fig. 4, we show a composite color image
with both g and r bands from HERON. This image is useful
for visualizing the full extent of the stream and its morphol-
ogy. The apparent size in length and width of 18.5 × 1 arcmin
by visual inspection corresponds to approximately 510 × 25 kpc
at the Coma distance. The middle panels of Fig. 4 show the
masking and subsequent binning (5 × 5 pixels, equivalent to
5.58 × 5.58 arcsec) of these data, allowing us to isolate the
stream from external sources. We can see that the stream has
a certain curvature. We estimate a radius of curvature of about
3620 arcsec, which is about 1◦
, and is equivalent to 1.7 Mpc.
The Coma virial radius is 2.4 Mpc (Ho et al. 2022). In the middle
panel of Fig. 4, we indicate with dashed lines the contours of an
annular aperture of 45 arcsec in width with this calculated radius
of curvature. This aperture is the width at which the stream is
detected in the HERON data, corresponding approximately to a
surface brightness of 30 mag arcsec−2
in the r band (the shallow-
est of the HERON data; see Sect. 2.1). This aperture is the same
as the one used in Sect. 3.2 to explore the potential IR emission
of the stream.
We use this aperture on the masked image to derive g and r
band photometric profiles along the stream, which are shown in
the lower panel of Fig. 4. Because of the strong fluctuations in
the profiles, we smooth them with a Gaussian kernel of approxi-
mately 10 binned pixel units in order to obtain a sufficient signal-
to-noise ratio (S/N) in the profile. We calibrate the zero-flux
sky level in the region adjacent to, but sufficiently far from, the
stream. We find average surface brightnesses along the stream
length of approximately 29.5 mag arcsec−2
in the g band and
29.0 mag arcsec−2
in the r band. The strong fluctuations of the
photometric profiles of the stream are due to the extremely low
surface brightness, together with the presence of masked regions,
but also to possible systematic effects such as background fluc-
tuation due to flat-fielding and sky subtraction.
Despite the obvious fluctuations, we observe that the differ-
ence between the g and r photometric profiles is relatively con-
stant. Figure 5 shows the distribution of pixel color values for
the stream. This latter faithfully follows a Gaussian function,
compatible with a constant color that would correspond to the
color of the stream. To obtain the average color and error, we
A157, page 6 of 14
7. Román, J., et al.: A&A 679, A157 (2023)
Fig. 4. Images and photometric profiles with HERON data. Top panel: composite color image with HERON in g and r bands. The high-contrast
gray background is constructed with the sum g + r image. Middle panels: high-contrast images in the same field as the top panel in g, g + r, and
r. Sources external to the stream were masked and the image was then rebinned to 5 × 5 pixels. The region bound by green dashed lines in the
g + r image marks the position of the stream. Bottom panel: surface brightness profiles of the stream along the aperture indicated in the g + r image.
HERON g and r bands are shown in blue and red, respectively, with an error of 1σ. Gray regions are spatial locations along the stream, which are
discarded due to the absence of signal produced by the masking from external sources.
calculate the mean value and error using a 3σ robust mean, yield-
ing g − r = 0.53 ± 0.05 mag. This color indirectly indicates that
a potential lensing of a high-redshift background source ampli-
fied by Coma can be ruled out, as a high-redshift source should
appear much redder in g − r color, and additionally, Coma is
too nearby to act effectively as a lens. In complement to this,
we fit the distribution with a Gaussian function that provides an
equivalent value (see Fig. 5). In order to obtain a pseudo color
g − L with which to relate the photometric magnitudes between
HERON (g and r bands) and WHT (L band), we constructed
an image with the average of the g and r bands. Using this
pseudo L band, we carried out a similar analysis, which yielded
g − L = 0.32 ± 0.03 mag.
We now focus on the analysis of the WHT data, with higher
nominal depth and better resolution, albeit only available in the
central region of the stream. Figure 6 shows a photometric pro-
file along the cross-section of the stream. The left panel shows a
high-contrast image binned 5 × 5 from the original pixel size of
0.2667 arcsec, giving at a pixel scale of 1.334 arcsec. The cen-
tral panel, shows this same image with masking applied to hide
A157, page 7 of 14
8. Román, J., et al.: A&A 679, A157 (2023)
-2 -1 0 1 2 3
g-r
0
5
10
15
Histogram
Fig. 5. Histogram of g − r color using HERON data at the selected
aperture for the Giant Coma Stream (see Fig. 4). The solid red line
shows the best fit to a Gaussian function. The dashed red vertical line
marks the mean color calculated with a 3σ resistant mean.
external sources to the stream. This masking is performed with a
combination of SExtractor, which aggressively hides mainly
sources of small sizes (DETECT_THRESH = 0.3), and a manual
masking with wide circular apertures hiding larger galaxies and
their expected haloes that could appear even below the surface
brightness detectable visibly in the images. After this masking,
the images are binned at 1.334 arcsec pix−1
, allowing the diffuse
light to emerge efficiently (see Román et al. 2021, for a similar
processing).
Given the nearly straight morphology of the stream in this
partial region, we project the combined flux in this direction,
obtaining a photometric profile along the cross-section. This is
done in the region of the image with a nominal depth of fainter
than 31.0 mag arcsec−2
in the L band (see Fig. A.1), avoiding the
outermost areas, which due to the dithering of the observations
have a lower S/N. The whole region shown in the central panel is
the one used for the photometric profile. For averaging, we use
the median value along the stream direction, with errors calcu-
lated as 1σ. We introduce a tilt plane that fits the sky background
in order to eliminate a small gradient present in the profile. The
obtained profile is smoothed with a three-pixel Gaussian kernel
to eliminate small fluctuations from the effects of masking.
The maximum surface brightness of the stream is approx-
imately 29.2 mag arcsec−2
in the L band. Using the previ-
ously calculated g − L color of 0.32 mag, this would trans-
late into a maximum surface brightness of approximately
29.5 mag arcsec−2
in the g band, agreeing with the values
obtained from the HERON data, and giving confidence to the
results. The WHT profile reaches reliably down to a surface
brightness of about 32 mag arcsec−2
, beyond which spurious
fluctuations begin to show up, probably due to sky fluctuations
and masking residuals. The shape of the profile is approximately
straight in its slope, and is therefore compatible with an exponen-
tial decay. By analyzing this profile in flux units, we can iden-
tify an approximately Gaussian shape (see Fig. 7). By modeling
this flux profile with a Gaussian function, the 1σ fitted width
has a value of 20.1 arcsec or 9.3 kpc. The FWHM is 42.3 arcsec
or 19.5 kpc. We notice a small asymmetry in the profile, where
on the left side (toward the direction where Coma is located)
the profile shows a slight excess. However, this asymmetry is
not strong, and is potentially caused by the masking residuals of
nearby galaxies located in that region.
Due to the numerous sources overlapping the stream, a direct
flux measurement is not possible. In order to obtain an inte-
grated magnitude, we use the good fit to a Gaussian profile to
model the total flux. To this end, we assume the average profile
to be that obtained in the analysis of Fig. 7 in order to integrate
it along the estimated length of 510 kpc (see Fig. 4). We con-
sider this a relatively good approximation because of the approx-
imately constant surface brightness along the entire length of
the stream. The value produced is L = 20.90 ± 0.12 mag, which
corresponds to g = 21.22 ± 0.15 mag according to the color g −
L = 0.32 ± 0.03 mag calculated above. The absolute magnitude
of the stream according to this model at the distance of Coma
would therefore be Lg = −13.78 ± 0.15 mag. Following mass
to light ratio predictions by Roediger & Courteau (2015), this
translates to a stellar mass of M? = 6.8 ± 0.8 × 107
M . We note
the potential presence of uncertainties on the integrated photo-
metric quantities, both because of systematic errors due to mod-
eling and possible nondetection of further structure in our data.
Therefore, integrated magnitudes are to be considered as order-
of-magnitude estimates, and as lower limits on the mass of both
the stream and its potential progenitor.
According to the predicted mass–metallicity relations for a
galaxy of this range of stellar mass (Panter et al. 2008; Simon
2019), a metallicity of approximately Z/H = −1 is expected. The
color g−r = 0.53 ± 0.05 mag would therefore indicate that this is
an old, passive dwarf galaxy according to single stellar popula-
tion models by Vazdekis et al. (2015; see also Román & Trujillo
2017).
4.2. Similar structures in simulations
To obtain an idea of how such structures could arise in ΛCDM,
we use the Illustris-TNG50 (TNG50 for short) simulations to
insight the existence of similar streams in clusters. The TNG50
simulation has a box size ∼50 Mpc on a side and a bary-
onic mass-per-particle of ∼8.5 × 104
M . TNG50 is part of the
Illustris-TNG suite of galaxy simulations in different volumes,
which all include gravity, magnetohydrodynamics, and a treat-
ment for the most relevant physical processes involved in galaxy
formation, such as star formation, metal enrichment, and stel-
lar and black hole feedback (Pillepich et al. 2018; Nelson et al.
2019).
It is difficult to estimate the frequency with which one should
expect to observe the kind of thin structure seen for the Giant
Coma Stream within the ΛCDM model. The formation of these
thin structures will depend primarily on two circumstances: tim-
ing of the merger or infall, and the intrinsic properties of the
progenitors. Tidal disruption that sets in too early with respect to
the present time at z = 0 – at which we analyze the cluster – or
progenitors that have overly extended intrinsic sizes will lead to
stellar streams that are too wide to be comparable to the Giant
Coma Stream. On the other hand, satellite infall that is too late or
intrinsic sizes that are too compact will lead to insufficient dis-
ruption to generate stellar streams that are as long as this stream.
While the relatively small box size in TNG50 does not allow
for clusters as massive as Coma to exist in the simulated vol-
ume, the high numerical resolution needed to resolve the inner
properties of the progenitors with an estimated mass of M? ∼
108−9
M makes the 50 Mpc box the most adequate to conduct
our analysis. From the TNG database, we use their friend-of-
friends group information to identify spatially coherent groups
A157, page 8 of 14
9. Román, J., et al.: A&A 679, A157 (2023)
Fig. 6. Surface-brightness images and profiles with the WHT data in the luminance filter. Left panel: binned image at a size of 5 × 5 pixels
(equivalent to 1.333 × 1.333 arcsec) color-coded in surface brightness and oriented so that the stream appears vertically. Middle panel: similar
to left panel but with all external sources masked and then binned to 5 × 5 pixels. Right panel: photometric profile in the luminance band L
(approximately equivalent to g + r) in the cross section (left-right) direction. The gray error regions correspond to 1σ. The widths in the transverse
direction of the three panels coincide in spatial scale.
Fig. 7. Photometric profile equivalent to that in the right panel of Fig. 6
but in arbitrary flux units. The dashed red line indicates the best fit to a
Gaussian function (see text). The gray error regions correspond to 1σ.
(Davis et al. 1985), the information about haloes and subhaloes
as provided by Subfind catalogs (Springel 2005; Dolag et al.
2009), and the SubLink merger trees (Rodriguez-Gomez et al.
2015).
The most massive cluster in TNG50 (group 0) has a virial
mass of M200 ∼ 2×1014
M and a virial radius of r200 ∼ 1200 kpc
(virial quantities are defined at the radius where the average
enclosed density is 200 times the critical density of the Uni-
verse). We note that the mass of Coma is approximately larger by
a factor of ten, M200 ∼ 2×1015
M (Ho et al. 2022), which means
that that even analyzing the highest-mass cluster in TNG50 falls
short of an appropriate comparison. Nevertheless, our use of the
TNG50 simulation is justified given the mass and spatial resolu-
tion needed to explore the presence of such narrow streams with
dwarf-mass progenitors as those inferred in our calculations.
In order to identify similar stream structures, we selected all
dwarf galaxies in the stellar mass range of M?,max = 108−9
M
that interacted with our group according to the SubLink merger
trees; we refer to these as progenitors. The selection is done at
the time of maximum stellar mass, M?,max. This gives us a total
of 342 progenitors for group 0. We then focused our search on
progenitors that have lost a significant fraction of their maximum
stellar content, f?,bound < 45%, where the bound fraction refers
to the fraction of stellar mass at z = 0 compared to the maxi-
mum stellar mass, because we are interested in progenitors of a
sizable stellar stream. This cut is used as it is close to but smaller
than half the maximum stellar mass of all satellites. In any case,
the exact value of the cut has little impact on our results. For
example, choosing all progenitors retaining 50% of their mass
would only add two objects to the sample, which were identified
to be accreted very late and to leave remnants at much larger dis-
tances than the observed structure. We therefore decided to keep
our 45% mass cut as a good proxy for our progenitors.
In addition, to identify progenitors that created structures fur-
ther out in the halo of the cluster, we require that the median
radius (r50) of the stellar debris, here simply defined as the mate-
rial that has been tidally removed according to our substructure
finder Subfind, be larger than 800 kpc. Our final sample com-
prises 19 progenitors. The main panel in Fig. 8 shows an image
created from the stellar debris of this sample.
Encouragingly, within this sample, we find one particular
stream with characteristics that are reminiscent of those of the
Giant Coma Stream. The analogous structure is highlighted in
A157, page 9 of 14
10. Román, J., et al.: A&A 679, A157 (2023)
Fig. 8. Projected map of stellar remnants from the identified dwarf progenitors with M?,max = 108−9
M that fell into the most massive group
simulated by the TNG50 simulation according to our selection criteria (see text). The map is color-coded by arbitrary surface brightness units,
with a resolution of 30 arcsec. The most prominent candidate for a Coma stream analog is highlighted, and the right panels show 2D projected
maps of only this remnant with a resolution of 1 arcsec (comparable to observational resolution).
cyan in the main panel of Fig. 8 and then shown in three perpen-
dicular projections in the smaller panels on the right. Not only is
this stream narrow and very extended as in the case of the Giant
Coma Stream, but also under the right projection it appears as an
almost straight line (when the projection is close to the orbital
plane). We note that the center of curvature of the stream points
toward the center of the cluster, as is the case for the Giant Coma
Stream. This could be considered as further evidence that indeed
the Giant Coma Stream belongs to Coma, because the approxi-
mate center of curvature coincides with the center of the gravi-
tational potential about which they orbit (Nibauer et al. 2023).
Our simulated analog has a progenitor stellar mass of
M?,max = 1.1 × 108
and has lost ∼75% of its original mass at the
present day, which is defined at snapshot 98 in the simulation,
or redshift z = 0.009. Interestingly, the formation history of this
stream is somewhat noncanonical, as the gravitational potential
of the clusters is not the only environment responsible for the
stellar stream formation. The tidal disruption leading to the for-
mation of this thin stream seems to start as part of preprocessing
in a smaller group environment. Our analog is first accreted into
another group with a virial mass of M200 = 5.48 × 1011
M at
infall time tinf = 2.98 Gyr (zinf = 2.2, defined as the last time this
dwarf galaxy was centered in its own dark matter halo). Only at
later times, by t = 6.5 Gyr, does the analog join the friends-of-
friends group of the main cluster, only crossing its virial radius
by t ∼ 12.7 Gyr, making it a relatively recent accretion. At
the final time, the analog has gone through only one pericen-
ter around the main cluster, from which it recently emerged and
is on its way to the first apocenter. The center of the group where
the preprocessing occurred is currently more than 1000 kpc away
from our analog.
The numerical resolution of TNG50 is insufficient to study
the morphology of the stream in detail, for example, in terms
of width or the light profile across the stream, for which hun-
dreds of thousands of stellar particles would be needed to faith-
fully trace the structure (compared to the ∼10 000 available in
TNG50 for this progenitor). Instead, this simulation provides a
idea of a possible formation scenario for very narrow and long
stellar streams in massive galaxy clusters, demonstrating that
they do occur within the current cosmological scenario. Tailored
idealized simulations would be the obvious next step to study
and understand the detailed properties of the stream in terms of
width, light profile, and color gradients.
5. Discussion
The properties of the Giant Coma Stream are remarkable. Its thin
and coherent morphology is reminiscent of cold stellar streams
observed in the Milky Way (e.g., Odenkirchen et al. 2003;
Grillmair & Dionatos 2006; Balbinot et al. 2016) or streams in
the Andromeda Galaxy (see a review by Ferguson & Mackey
2016). Its surface brightness peaks at a very faint level of
29.5 mag arcsec−2
in the g band (see Fig. 6), which is com-
parable to the surface brightness of the Giant Stream in the
Andromeda Galaxy (Ibata et al. 2001). However, the size of the
Giant Coma Stream, with a detected length of approximately
510 kpc, is longer than any known “giant” stream in the literature
(Ibata et al. 2001; Martínez-Delgado et al. 2009, 2021, 2023b).
To the best of our knowledge, no stellar stream of such size has
ever been detected, nor has a stream of such low surface bright-
ness been seen in surface photometry observations.
A157, page 10 of 14
11. Román, J., et al.: A&A 679, A157 (2023)
Previous work in Coma and other galaxy clusters revealed
the presence of tidally disrupted objects (Trentham & Mobasher
1998; Gregg & West 1998; Conselice & Gallagher 1999;
Calcáneo-Roldán et al. 2000) showing evidence for the build
up of the intracluster light by accretion of substructures.
We now discuss some particular cases. First, the plume-like
object discovered by Gregg & West (1998) in the heart of
Coma is 130 kpc long and about 15−30 kpc wide. Its surface
brightness is much brighter (µR = 25.7 mag arcsec−2
) than
that of the Giant Coma Stream, as is its integrated luminos-
ity (R = 15.6 ± 0.1 mag), and it is of a much redder color,
namely g − r ≈ 0.75 mag (Gregg & West 1998). A simple
calculation shows that the stellar mass of this plume-like
object is approximately 1010
solar masses, indicating that the
remnant is a much more massive galaxy than a dwarf, and
is probably an elliptical galaxy, discarding a common origin.
While the properties and locations of this plume-like object
and the Giant Coma Stream differ, it is interesting that both
share the same orientation, and that this orientation coincides
in their alignment with the main filament that feeds Coma (see
Malavasi et al. 2020). Additionally, correlated accretion due to
the orientation of filaments and large-scale structure is expected
to occur within ΛCDM (e.g., Libeskind et al. 2014). Another
interesting object is the arc located in the Centaurus cluster
discovered by Calcáneo-Roldán et al. (2000). Its morphology
is remarkably similar to that of the Giant Coma Stream, with
a linear and featureless appearance, and a length of ∼170 kpc
(Calcáneo-Roldán et al. 2000). However, the surface brightness
is considerably higher than that of the Giant Coma Stream with
µR = 26.1 mag arcsec−2
. Calcáneo-Roldán et al. (2000) argue
that this object could be a tidally disrupted luminous spiral
galaxy.
Several more recent studies have been carried out in a num-
ber of galaxy clusters (Giallongo et al. 2014; Montes & Trujillo
2018, 2022; DeMaio et al. 2018; Montes et al. 2021; Jiménez-
Teja et al. 2021). The surface brightness and resolution (due to
the close proximity of the Coma cluster) achieved in our work
are unprecedented, with one exception. The Burrell Schmidt
Deep Virgo Survey (Mihos et al. 2017) is comparable in terms
of depth to our observations with the addition of a better reso-
lution due to the proximity of the Virgo Cluster. Indeed, a large
number of thin stellar streams appear in the central region of
Virgo; for example, a pair of streams to the NW of M87 with
lengths of around 150 kpc and similarly thin morphologies and
widths of on the order of tens of kiloparsecs (streams A and B
by Mihos et al. 2005; Rudick et al. 2010), as well as a myriad of
much smaller streams or tidal features associated with different
galaxies in the field of Virgo (Mihos et al. 2017).
A fundamental characteristic that differentiates the Giant
Coma Stream from the streams detected in Virgo is that it
is not associated with any particular galaxy but is a free-
floating structure in the external regions of Coma. Dynami-
cally cold and extremely faint stellar streams are thought to
form through strong tidal fields in low-mass accretion events
(Bullock & Johnston 2005), and in the case of galaxy clus-
ters through interactions of low-mass galaxies passing through
the inner region of the clusters (Romanowsky et al. 2012;
Cooper et al. 2015). These streams are fragile, and dynamical
times of one or two times the crossing time are enough to destroy
them (Rudick et al. 2009). It is therefore striking that the Giant
Coma Stream is a free-floating stream far from the center of the
cluster, with such a coherent and fragile morphology.
We argue that the lack of detected free-floating streams in
Virgo could be due to two factors. First, Coma is much more
massive than Virgo, which implies a much higher velocity dis-
persion, σv = 1008 km s−1
for Coma (Struble & Rood 1999) ver-
sus σv = 638 km s−1
for Virgo (Kashibadze et al. 2020), and so
high-velocity galaxies are more common in Coma. Second, a
free-floating stream in Virgo would be expected to lie in the
periphery of the cluster, but due to the proximity of Virgo, the
deep data provided by Mihos et al. (2017) are limited to its cen-
tral region. If a similar feature exists at a projected distance of
the Giant Coma Stream, namely 0.8 Mpc, in Virgo, that stream
would be outside the footprint of these observations and there-
fore undetected. This makes it potentially interesting to explore
the outermost regions of the Virgo cluster or other nearby clus-
ters in a search for similar free-floating streams analogous to the
Giant Coma Stream.
The presence of an analog stream in the TNG-50 simula-
tion may indicate that such free-floating streams with cold or
thin morphology may be common in galaxy clusters. There is
no guarantee that the Giant Coma Stream was formed by a com-
plex interaction like the one depicted by our analog. However,
it is encouraging that we find at least one analog in the forma-
tion history of a galaxy cluster. Our analysis indicates that while
typical debris from this type of progenitor tends to be wider and
less coherent than the Giant Coma Stream, at least there is one
case where the narrowness and length of the stellar stream are
comparable to it, suggesting that such structures may occur in
ΛCDM. The recent accretion of this analog is compatible with
the fragility of this type of structure, which, as mentioned above,
is typically able to survive only one or two times the crossing
time in its orbit by the cluster, making it very likely that the Giant
Coma Stream is a recent accretion.
The potential presence of such thin stellar streams of cold
morphology in galaxy clusters could extend the environmen-
tal range of their study from galactic to cluster scales. If cold
stellar streams of considerably larger sizes than those found in
the Local Group were found to be common, this would make
current projections of their detectability much more optimistic
(Pearson et al. 2019), and future observational work, including
by Euclid, the Rubin Observatory, the Nancy Grace Roman
Space Telescope or ARRAKIHS, will be necessary in order to
unveil similar structures in galaxy clusters and the properties of
both the Giant Coma Stream and potential new discoveries.
One of the imminent and most impactfull applications of
the study of cold stellar streams is related to the possibility of
testing the shapes of the dark matter haloes and the subhalo
distribution in their hosts, as the presence and number of sub-
haloes is ultimately defined by the properties of dark matter
particles (Ibata et al. 2002; Carlberg 2012; Erkal & Belokurov
2015). Ongoing work includes the analysis of the morphology
and kinematics of cold stellar streams in the Milky Way, with
the objective of tracing the global gravitational potential and
also analyzing the possible impact of a low-mass dark mat-
ter subhalo that could perturb these streams both morphologi-
cally and kinematically (Erkal et al. 2016; Banik & Bovy 2019;
Ibata et al. 2020; Banik et al. 2021).
The available observational data for the Giant Coma Stream
are insufficient in both resolution and depth and therefore do not
allow a detailed analysis of this stream. We recall that the maxi-
mum resolution of our data is approximately 1.2 arcsec FWHM,
which is equivalent to 550 pc at the Coma distance. Additionally,
radial velocity measurements of individual stars are fundamental
to these analyses (Pearson et al. 2022). While current instrumen-
tal capabilities do not allow for such analyses, the new genera-
tion of extremely large-aperture telescopes may have sufficient
observational capabilities for these studies.
A157, page 11 of 14
12. Román, J., et al.: A&A 679, A157 (2023)
6. Summary
In this work, we report the discovery of the Giant Coma Stream,
a stellar stream with an extremely coherent and thin morphology,
located at a distance of 0.8 Mpc from the center of the Coma
cluster, and reminiscent of the cold stellar streams detected in
the Milky Way.
– The properties of the Giant Coma Stream are striking: a
maximum surface brightness of µg = 29.5 mag arcsec−2
and
a length of 510 kpc. This makes it the faintest stream ever
detected by surface photometry. The stellar mass is esti-
mated to be M? = 6.8 ± 0.8 × 107
M with a color of g −
r = 0.53 ± 0.05 mag, which is consistent with a passive dwarf
galaxy being the potential progenitor for the Giant Coma
Stream. We do not identify any potential galaxy remnant
or core, and the stream structure appears featureless in our
data.
– The Giant Coma Stream is orders of magnitude fainter
in surface brightness than previous tidal features discov-
ered in Coma and other clusters (Trentham & Mobasher
1998; Gregg & West 1998; Conselice & Gallagher 1999;
Calcáneo-Roldán et al. 2000). It is comparable in surface
brightness to the thin streams detected in Virgo (Mihos et al.
2017), however unlike these, the Giant Coma Stream does
not appear to be associated with any particular galaxy,
appearing as a free-floating feature in the outer regions of
Coma.
– Through analysis of the Illustris-TNG50 simulation, we find
a remarkably similar analog, suggesting that such giant,
extremely faint, and free-floating thin stellar streams may
exist in galaxy clusters according to Λ-CDM.
This work shows a glimpse of the kind of structures waiting
to be discovered in the ultralow-surface-brightness Universe.
These structures, such as the Giant Coma Stream, show promis-
ing properties in revealing the ongoing hierarchical assembly of
galaxy clusters and potentially unveiling the ultimate nature of
dark matter.
Acknowledgements. We thank the two anonymous referees for a thorough
review of our work. We thank Chris Mihos, Garreth William Martin and Clau-
dio Dalla Vecchia for interesting discussions about the result. We acknowl-
edge financial support from the State Research Agency (AEI-MCINN) of
the Spanish Ministry of Science and Innovation under the grant “The struc-
ture and evolution of galaxies and their central regions” with reference
PID2019-105602GB-I00/10.13039/501100011033, from the ACIISI, Consejería
de Economía, Conocimiento y Empleo del Gobierno de Canarias and the
European Regional Development Fund (ERDF) under grant with reference
PROID2021010044, and from IAC project P/300724, financed by the Min-
istry of Science and Innovation, through the State Budget and by the Canary
Islands Department of Economy, Knowledge and Employment, through the
Regional Budget of the Autonomous Community. J.R. acknowledges funding
from University of La Laguna through the Margarita Salas Program from the
Spanish Ministry of Universities ref. UNI/551/2021-May 26, and under the EU
Next Generation. R.M.R. acknowledges financial support from his late father
Jay Baum Rich. I.T. and G.G. acknowledge support from the ACIISI, Con-
sejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and
the European Regional Development Fund (ERDF) under grant with refer-
ence PROID2021010044 and from the State Research Agency (AEI-MCINN)
of the Spanish Ministry of Science and Innovation under the grant PID2019-
107427GB-C32 and IAC project P/302300, financed by the Ministry of Science
and Innovation, through the State Budget and by the Canary Islands Depart-
ment of Economy, Knowledge and Employment, through the Regional Bud-
get of the Autonomous Community. The operation of the Jeanne Rich Tele-
scope was assisted by David Gedalia and Osmin Caceres and is hosted by the
Polaris Observatory Association. This work is based on service observations
made with the William Herschel Telescope (programme SW2021a15) operated
on the island of La Palma by the Isaac Newton Group of Telescopes in the Span-
ish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de
Canarias.
References
Akeson, R., Armus, L., Bachelet, E., et al. 2019, arXiv e-prints
[arXiv:1902.05569]
Balbinot, E., Yanny, B., Li, T. S., et al. 2016, ApJ, 820, 58
Banik, N., & Bovy, J. 2019, MNRAS, 484, 2009
Banik, N., Bovy, J., Bertone, G., et al. 2021, JCAP, 2021, 043
Belokurov, V., Zucker, D. B., Evans, N. W., et al. 2006, ApJ, 642, L137
Bertin, E. 2006, ASP Conf. Ser., 351, 112
Bertin, E., Mellier, Y., Radovich, M., et al. 2002, ASP Conf. Proc., 281, 228
Biviano, A. 1998, Untangling Coma Berenices: A New Vision of an Old Cluster,
1
Bonaca, A., & Hogg, D. W. 2018, ApJ, 867, 101
Bonafede, A., Brunetti, G., Rudnick, L., et al. 2022, ApJ, 933, 218
Bullock, J. S., & Johnston, K. V. 2005, ApJ, 635, 931
Calcáneo-Roldán, C., Moore, B., Bland-Hawthorn, J., et al. 2000, MNRAS, 314,
324
Carlberg, R. G. 2012, ApJ, 748, 20
Conselice, C. J., & Gallagher, J. S. 1999, AJ, 117, 75
Cooper, A. P., Cole, S., Frenk, C. S., et al. 2010, MNRAS, 406, 744
Cooper, A. P., Gao, L., Guo, Q., et al. 2015, MNRAS, 451, 2703
Crnojević, D., Sand, D. J., Spekkens, K., et al. 2016, ApJ, 823, 19
Davis, M., Efstathiou, G., Frenk, C. S., et al. 1985, ApJ, 292, 371
DeMaio, T., Gonzalez, A. H., Zabludoff, A., et al. 2015, MNRAS, 448, 1162
DeMaio, T., Gonzalez, A. H., Zabludoff, A., et al. 2018, MNRAS, 474, 3009
Dey, A., Schlegel, D. J., Lang, D., et al. 2019, AJ, 157, 168
Dolag, K., Borgani, S., Murante, G., et al. 2009, MNRAS, 399, 497
Dodd, E., Callingham, T. M., Helmi, A., et al. 2023, A&A, 670, L2
Dubinski, J., Mihos, J. C., & Hernquist, L. 1999, ApJ, 526, 607
Duc, P.-A., Cuillandre, J.-C., Karabal, E., et al. 2015, MNRAS, 446, 120
Erkal, D., & Belokurov, V. 2015, MNRAS, 454, 3542
Erkal, D., Belokurov, V., Bovy, J., et al. 2016, MNRAS, 463, 102
Euclid Collaboration (Scaramella, R., et al.) 2022a, A&A, 662, A112
Euclid Collaboration (Borlaff, A. S., et al.) 2022b, A&A, 657, A92
Feretti, L., Giovannini, G., Govoni, F., et al. 2012, A&ARv, 20, 54
Ferguson, A. M. N., & Mackey, A. D. 2016, Tidal Streams in the Local Group
and Beyond (Cham: Springer)
Genina, A., Deason, A. J., & Frenk, C. S. 2023, MNRAS, 520, 3767
Giallongo, E., Menci, N., Grazian, A., et al. 2014, ApJ, 781, 24
Gregg, M. D., & West, M. J. 1998, Nature, 396, 549
Grillmair, C. J., & Dionatos, O. 2006, ApJ, 643, L17
Gu, M., Conroy, C., Law, D., et al. 2020, ApJ, 894, 32
Helmi, A. 2020, ARA&A, 58, 205
Ho, M., Ntampaka, M., Rau, M. M., et al. 2022, Nat. Astron., 6, 936
Ibata, R., Irwin, M., Lewis, G., et al. 2001, Nature, 412, 49
Ibata, R. A., Lewis, G. F., Irwin, M. J., et al. 2002, MNRAS, 332, 915
Ibata, R., Thomas, G., Famaey, B., et al. 2020, ApJ, 891, 161
Ibata, R., Malhan, K., Martin, N., et al. 2021, ApJ, 914, 123
Ivezić, Ž., Kahn, S. M., Tyson, J. A., et al. 2019, ApJ, 873, 111
Jee, M. J., Stroe, A., Dawson, W., et al. 2015, ApJ, 802, 46
Jiménez-Teja, Y., Dupke, R. A., Lopes de Oliveira, R., et al. 2019, A&A, 622,
A183
Jiménez-Teja, Y., Vílchez, J. M., Dupke, R. A., et al. 2021, ApJ, 922, 268
Johnston, K. V., Zhao, H., Spergel, D. N., et al. 1999, ApJ, 512, L109
Johnston, K. V., Bullock, J. S., Sharma, S., et al. 2008, ApJ, 689, 936
Kashibadze, O. G., Karachentsev, I. D., & Karachentseva, V. E. 2020, A&A, 635,
A135
Kelvin, L. S., Hasan, I., & Tyson, J. A. 2023, MNRAS, 520, 2484
Knapen, J. H., & Trujillo, I. 2017, Astrophys. Space Sci. Lib., 434, 255
Kourkchi, E., & Tully, R. B. 2017, ApJ, 843, 16
Lang, D., Hogg, D. W., Mierle, K., et al. 2010, AJ, 139, 1782
Libeskind, N. I., Knebe, A., Hoffman, Y., et al. 2014, MNRAS, 443, 1274
Liu, M. C., & Graham, J. R. 2001, ApJ, 557, L31
Low, F. J., Beintema, D. A., Gautier, T. N., et al. 1984, ApJ, 278, L19
Mackey, D., Lewis, G. F., Brewer, B. J., et al. 2019, Nature, 574, 69
Malavasi, N., Aghanim, N., Tanimura, H., et al. 2020, A&A, 634, A30
Marchuk, A. A., Smirnov, A. A., Mosenkov, A. V., et al. 2021, MNRAS, 508,
5825
Martin, G., Bazkiaei, A. E., Spavone, M., et al. 2022, MNRAS, 513, 1459
Martínez-Delgado, D., Pohlen, M., Gabany, R. J., et al. 2009, ApJ, 692, 955
Martínez-Delgado, D., Gabany, R. J., Crawford, K., et al. 2010, AJ, 140, 962
Martínez-Delgado, D., Román, J., Erkal, D., et al. 2021, MNRAS, 506, 5030
Martínez-Delgado, D., Cooper, A. P., Román, J., et al. 2023a, A&A, 671, A141
Martínez-Delgado, D., Roca-Fàbrega, S., Miró-Carretero, J., et al. 2023b, A&A,
669, A103
McConnachie, A. W., Ibata, R., Martin, N., et al. 2018, ApJ, 868, 55
Mihos, J. C. 2019, arXiv e-prints [arXiv:1909.09456]
Mihos, J. C., Harding, P., Feldmeier, J., et al. 2005, ApJ, 631, L41
A157, page 12 of 14
13. Román, J., et al.: A&A 679, A157 (2023)
Mihos, J. C., Harding, P., Feldmeier, J. J., et al. 2017, ApJ, 834, 16
Monachesi, A., Gómez, F. A., Grand, R. J. J., et al. 2019, MNRAS, 485, 2589
Montes, M. 2022, Nat. Astron., 6, 308
Montes, M., & Trujillo, I. 2018, MNRAS, 474, 917
Montes, M., & Trujillo, I. 2022, ApJ, 940, L51
Montes, M., Brough, S., Owers, M. S., et al. 2021, ApJ, 910, 45
Mouhcine, M., Ibata, R., & Rejkuba, M. 2010, ApJ, 714, L12
Nelson, D., Springel, V., Pillepich, A., et al. 2019, Comput. Astrophys. Cosmol.,
6, 2
Neugebauer, G., Habing, H. J., van Duinen, R., et al. 1984, ApJ, 278, L1
Nibauer, J., Bonaca, A., & Johnston, K. V. 2023, ApJ, 954, 195
Odenkirchen, M., Grebel, E. K., Dehnen, W., et al. 2003, AJ, 126, 2385
Panter, B., Jimenez, R., Heavens, A. F., et al. 2008, MNRAS, 391, 1117
Pearson, S., Starkenburg, T. K., Johnston, K. V., et al. 2019, ApJ, 883, 87
Pearson, S., Price-Whelan, A. M., Hogg, D. W., et al. 2022, ApJ, 941, 19
Pilbratt, G. L., Riedinger, J. R., Passvogel, T., et al. 2010, A&A, 518, L1
Pillepich, A., Vogelsberger, M., Deason, A., et al. 2014, MNRAS, 444, 237
Pillepich, A., Nelson, D., Hernquist, L., et al. 2018, MNRAS, 475, 648
Planck Collaboration XXIV. 2011, A&A, 536, A24
Planck Collaboration VI. 2020, A&A, 641, A6
Reino, S., Rossi, E. M., Sanderson, R. E., et al. 2021, MNRAS, 502, 4170
Rejkuba, M. 2012, Ap&SS, 341, 195
Rey, M. P., & Starkenburg, T. K. 2022, MNRAS, 510, 4208
Rodriguez-Gomez, V., Genel, S., Vogelsberger, M., et al. 2015, MNRAS, 449,
49
Rich, R. M., Collins, M. L. M., Black, C. M., et al. 2012, Nature, 482, 192
Rich, R. M., Brosch, N., Bullock, J., et al. 2017, IAU Symp., 321, 186
Rich, R. M., Mosenkov, A., Lee-Saunders, H., et al. 2019, MNRAS, 490, 1539
Roediger, J. C., & Courteau, S. 2015, MNRAS, 452, 3209
Román, J., & Trujillo, I. 2017, MNRAS, 468, 4039
Román, J., Trujillo, I., & Montes, M. 2020, A&A, 644, A42
Román, J., Castilla, A., & Pascual-Granado, J. 2021, A&A, 656, A44
Romanowsky, A. J., Strader, J., Brodie, J. P., et al. 2012, ApJ, 748, 29
Rudick, C. S., Mihos, J. C., Frey, L. H., et al. 2009, ApJ, 699, 1518
Rudick, C. S., Mihos, J. C., Harding, P., et al. 2010, ApJ, 720, 569
Sanders, J. L., & Binney, J. 2013, MNRAS, 433, 1826
Schlafly, E. F., & Finkbeiner, D. P. 2011, ApJ, 737, 103
Simon, J. D. 2019, ARA&A, 57, 375
Smirnov, A. A., Savchenko, S. S., Poliakov, D. M., et al. 2023, MNRAS, 519,
4735
Springel, V. 2005, MNRAS, 364, 1105
Struble, M. F., & Rood, H. J. 1999, ApJS, 125, 35
Tal, T., van Dokkum, P. G., Nelan, J., et al. 2009, AJ, 138, 1417
Trentham, N., & Mobasher, B. 1998, MNRAS, 293, 53
Trujillo, I., D’Onofrio, M., Zaritsky, D., et al. 2021, A&A, 654, A40
van Weeren, R. J., de Gasperin, F., Akamatsu, H., et al. 2019, Space Sci. Rev.,
215, 16
Vazdekis, A., Coelho, P., Cassisi, S., et al. 2015, MNRAS, 449, 1177
Veneziani, M., Ade, P. A. R., Bock, J. J., et al. 2010, ApJ, 713, 959
Zackrisson, E., de Jong, R. S., & Micheva, G. 2012, MNRAS, 421, 190
Zwicky, F. 1933, Helv. Phys. Acta, 6, 110
Zwicky, F. 1951, PASP, 63, 61
A157, page 13 of 14
14. Román, J., et al.: A&A 679, A157 (2023)
Appendix A: Exposure times and depth in the WHT
data
The left panel of Fig. A.1 shows the exposure time footprint for
the WHT data. In order to provide a map of surface brightness
limits, we performed the correlation between the standard devi-
ation for pixels with equal exposure time and the exposure time.
This correlation is shown graphically in Fig. A.2. The parame-
ters of the best fit are
µlim,L = −2.55 × log
1
p
texp[h]
+ 30.13 mag arcsec−2
,
measured as 3σ in 10×10 arcsec boxes. By means of this
obtained relation, we can make a surface brightness map using
the exposure time values for each pixel. This map is shown in
the right panel of Fig. A.1.
Fig. A.1. Maps of exposure time (left panel) and equivalent limiting surface brightness (right panel) for the WHT data in the luminance band
(equivalent to g + r SDSS filters). Images cover a 14.15 x 17.67 arcmin rectangle. North is up, east to the left.
Fig. A.2. Linear correlation between exposure time and surface
brightness limits measured as 3σ in 10×10 arcsec boxes for the
WHT data. The blue line marks the correlation data obtained. The
black dashed line marks the best fit of the correlation (see text).
A157, page 14 of 14