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.
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.
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.
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 a study that estimates the dynamical surface mass density between 1.5 and 4 kpc from the Galactic plane using kinematics of thick disk stars. The authors derive an exact analytical expression for the surface density based on assumptions about the stellar population and Galactic potential. Their expression matches expectations of visible mass alone, with no evidence for additional dark matter required. They extrapolate a local dark matter density of 0±1 mM⊙ pc−3, excluding all current spherical dark matter halo models at over 4σ confidence. Only a highly prolate dark matter halo could potentially reconcile the observations with models, but this is unlikely according to ΛCDM.
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
This document describes the discovery of a giant ring-like structure in the observable universe displayed by 9 gamma ray bursts (GRBs) between redshifts of 0.78 and 0.86. The ring has a diameter of 1720 Mpc, over five times larger than the expected transition scale to homogeneity. The ring lies at a distance of 2770 Mpc with major and minor diameters of 43° and 30°, respectively. The probability of this structure occurring by random chance is calculated to be 2 × 10-6. This ring-shaped feature contradicts the cosmological principle of large-scale homogeneity and isotropy, and the physical mechanism responsible is unknown.
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
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
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 first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
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.
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.
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 a study that estimates the dynamical surface mass density between 1.5 and 4 kpc from the Galactic plane using kinematics of thick disk stars. The authors derive an exact analytical expression for the surface density based on assumptions about the stellar population and Galactic potential. Their expression matches expectations of visible mass alone, with no evidence for additional dark matter required. They extrapolate a local dark matter density of 0±1 mM⊙ pc−3, excluding all current spherical dark matter halo models at over 4σ confidence. Only a highly prolate dark matter halo could potentially reconcile the observations with models, but this is unlikely according to ΛCDM.
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
This document describes the discovery of a giant ring-like structure in the observable universe displayed by 9 gamma ray bursts (GRBs) between redshifts of 0.78 and 0.86. The ring has a diameter of 1720 Mpc, over five times larger than the expected transition scale to homogeneity. The ring lies at a distance of 2770 Mpc with major and minor diameters of 43° and 30°, respectively. The probability of this structure occurring by random chance is calculated to be 2 × 10-6. This ring-shaped feature contradicts the cosmological principle of large-scale homogeneity and isotropy, and the physical mechanism responsible is unknown.
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
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
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 first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
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 physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
The extremely high albedo of LTT 9779 b revealed by CHEOPSSérgio Sacani
Optical secondary eclipse measurements of small planets can provide a wealth of information about the reflective properties
of these worlds, but the measurements are particularly challenging to attain because of their relatively shallow depth. If such signals
can be detected and modeled, however, they can provide planetary albedos, thermal characteristics, and information on absorbers in
the upper atmosphere.
Aims. We aim to detect and characterize the optical secondary eclipse of the planet LTT 9779 b using the CHaracterising ExOPlanet
Satellite (CHEOPS) to measure the planetary albedo and search for the signature of atmospheric condensates.
Methods. We observed ten secondary eclipses of the planet with CHEOPS. We carefully analyzed and detrended the light curves using
three independent methods to perform the final astrophysical detrending and eclipse model fitting of the individual and combined light
curves.
Results. Each of our analysis methods yielded statistically similar results, providing a robust detection of the eclipse of LTT 9779 b
with a depth of 115±24 ppm. This surprisingly large depth provides a geometric albedo for the planet of 0.80+0.10
−0.17, consistent with
estimates of radiative-convective models. This value is similar to that of Venus in our own Solar System. When combining the eclipse
from CHEOPS with the measurements from TESS and Spitzer, our global climate models indicate that LTT 9779 b likely has a super
metal-rich atmosphere, with a lower limit of 400× solar being found, and the presence of silicate clouds. The observations also reveal
hints of optical eclipse depth variability, but these have yet to be confirmed.
Conclusions. The results found here in the optical when combined with those in the near-infrared provide the first steps toward
understanding the atmospheric structure and physical processes of ultrahot Neptune worlds that inhabit the Neptune desert.
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
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.
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.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
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.
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.
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
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
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
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.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
More Related Content
Similar to An almost dark galaxy with the mass of the Small Magellanic Cloud
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 physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
The extremely high albedo of LTT 9779 b revealed by CHEOPSSérgio Sacani
Optical secondary eclipse measurements of small planets can provide a wealth of information about the reflective properties
of these worlds, but the measurements are particularly challenging to attain because of their relatively shallow depth. If such signals
can be detected and modeled, however, they can provide planetary albedos, thermal characteristics, and information on absorbers in
the upper atmosphere.
Aims. We aim to detect and characterize the optical secondary eclipse of the planet LTT 9779 b using the CHaracterising ExOPlanet
Satellite (CHEOPS) to measure the planetary albedo and search for the signature of atmospheric condensates.
Methods. We observed ten secondary eclipses of the planet with CHEOPS. We carefully analyzed and detrended the light curves using
three independent methods to perform the final astrophysical detrending and eclipse model fitting of the individual and combined light
curves.
Results. Each of our analysis methods yielded statistically similar results, providing a robust detection of the eclipse of LTT 9779 b
with a depth of 115±24 ppm. This surprisingly large depth provides a geometric albedo for the planet of 0.80+0.10
−0.17, consistent with
estimates of radiative-convective models. This value is similar to that of Venus in our own Solar System. When combining the eclipse
from CHEOPS with the measurements from TESS and Spitzer, our global climate models indicate that LTT 9779 b likely has a super
metal-rich atmosphere, with a lower limit of 400× solar being found, and the presence of silicate clouds. The observations also reveal
hints of optical eclipse depth variability, but these have yet to be confirmed.
Conclusions. The results found here in the optical when combined with those in the near-infrared provide the first steps toward
understanding the atmospheric structure and physical processes of ultrahot Neptune worlds that inhabit the Neptune desert.
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
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.
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.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
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.
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.
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
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
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
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.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
Similar to An almost dark galaxy with the mass of the Small Magellanic Cloud (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
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.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
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.
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
CLASS 12th CHEMISTRY SOLID STATE ppt (Animated)eitps1506
Description:
Dive into the fascinating realm of solid-state physics with our meticulously crafted online PowerPoint presentation. This immersive educational resource offers a comprehensive exploration of the fundamental concepts, theories, and applications within the realm of solid-state physics.
From crystalline structures to semiconductor devices, this presentation delves into the intricate principles governing the behavior of solids, providing clear explanations and illustrative examples to enhance understanding. Whether you're a student delving into the subject for the first time or a seasoned researcher seeking to deepen your knowledge, our presentation offers valuable insights and in-depth analyses to cater to various levels of expertise.
Key topics covered include:
Crystal Structures: Unravel the mysteries of crystalline arrangements and their significance in determining material properties.
Band Theory: Explore the electronic band structure of solids and understand how it influences their conductive properties.
Semiconductor Physics: Delve into the behavior of semiconductors, including doping, carrier transport, and device applications.
Magnetic Properties: Investigate the magnetic behavior of solids, including ferromagnetism, antiferromagnetism, and ferrimagnetism.
Optical Properties: Examine the interaction of light with solids, including absorption, reflection, and transmission phenomena.
With visually engaging slides, informative content, and interactive elements, our online PowerPoint presentation serves as a valuable resource for students, educators, and enthusiasts alike, facilitating a deeper understanding of the captivating world of solid-state physics. Explore the intricacies of solid-state materials and unlock the secrets behind their remarkable properties with our comprehensive presentation.
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.
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
BIRDS DIVERSITY OF SOOTEA BISWANATH ASSAM.ppt.pptxgoluk9330
Ahota Beel, nestled in Sootea Biswanath Assam , is celebrated for its extraordinary diversity of bird species. This wetland sanctuary supports a myriad of avian residents and migrants alike. Visitors can admire the elegant flights of migratory species such as the Northern Pintail and Eurasian Wigeon, alongside resident birds including the Asian Openbill and Pheasant-tailed Jacana. With its tranquil scenery and varied habitats, Ahota Beel offers a perfect haven for birdwatchers to appreciate and study the vibrant birdlife that thrives in this natural refuge.
2. A&A proofs: manuscript no. dgs82
ably (see e.g., Sandage & Binggeli 1984; Conselice et al. 2003;
van Dokkum et al. 2015; Román & Trujillo 2017; Lim et al.
2020; Tanoglidis et al. 2021; Trujillo et al. 2021; Marleau et al.
2021; La Marca et al. 2022; Zaritsky et al. 2023), and it is ex-
pected to continue to increase with the arrival of very deep opti-
cal surveys (see e.g., Ivezić et al. 2019). Within this population
of very faint galaxies, the so-called “almost dark" galaxies are
of particular interest. These faint galaxies are missed in the op-
tical catalogues of wide field surveys such as the Sloan Digital
Sky Survey (SDSS, Eisenstein et al. 2011). Although there is
no definition of the surface brightness of an almost dark galaxy,
given the SDSS surface brightness limit (i.e., µr ∼ 26.5 − 27
mag/arcsec2
; 3σ in 10′′
×10′′
boxes), galaxies with central sur-
face brightness fainter than µr(0) ∼ 26 mag/arcsec2
are very dif-
ficult to detect in SDSS catalogues. Therefore, we can use such a
value as a rough definition of what an almost dark galaxy should
be. These galaxies represent less than 1% of the galaxies found
in blind HI surveys such as Arecibo Legacy Fast Arecibo L-band
Feed Array (ALFALFA, Giovanelli et al. 2005), and have HI
masses between 107
and 109
M⊙. Since the definition of an al-
most dark galaxy depends on whether it is typically detected in
the SDSS, its maximum stellar surface mass density is a func-
tion of its stellar population properties (age and metallicity). In a
scenario where the age of the stellar population is old (∼ 10 Gyr)
and metal-poor ([Fe/H]∼ −1), a surface brightness of µr(0) ∼ 26
mag/arcsec2
corresponds to a few M⊙/pc2
. This is very close to
the expected stellar surface density resulting from the gas density
threshold for star formation (Schaye 2004) and in good agree-
ment with the values found at the edges of galaxies where star
formation suddenly drops off (Trujillo et al. 2020; Chamba et al.
2022). Consequently, almost dark galaxies may also be an inter-
esting place to study how galaxy formation occurs at low densi-
ties.
In this paper, we describe the structural properties of a very
extended almost dark galaxy serendipitously discovered in the
IAC Stripe82 Legacy Project (Fliri & Trujillo 2016; Román &
Trujillo 2018). This object (which we have named Nube1
) was
found during a visual inspection of one of the survey fields. The
object is not visible in SDSS and appears quite noisy even in
deeper images such as those produced by the Stripe82 data (see
Fig. 1). Dedicated observations with the Gran Telescopio Ca-
narias and the Green Bank Telescope have allowed to charac-
terise its nature in detail. This paper presents a comprehensive
analysis of the stellar populations and structural properties of this
object. We also consider the properties of this very faint galaxy
within the cold dark matter and fuzzy dark matter scenarios.
Throughout this work we adopt a standard cosmological
model with the following parameters: H0 = 70 km s−1
Mpc−1
,
Ωm = 0.3 and ΩΛ = 0.7. Based on the probable redshift of this
galaxy, the assumed distance is 107 Mpc, corresponding to a spa-
tial scale of 0.5039 kpc/arcsec. All magnitudes in this paper are
in the AB magnitude system.
2. Data
The data used in this paper come from two different facilities: the
10.4m Gran Telescopio Canarias (GTC) and the 100m Robert C.
Byrd Green Bank Telescope (GBT). The details of each obser-
vation are described below.
1
noo-beh. Cloud in Spanish.
2.1. GTC HiPERCAM images
Deep optical multi-band imaging of Nube was performed using
HiPERCAM. HiPERCAM (Dhillon et al. 2018) is a quintuple-
beam, high-speed astronomical imager capable of simultane-
ously imaging celestial objects in five different Sloan filters (u,
g, r, i, z). The image area of each of the five CCDs is 2048×1024
pixels (2.7′
× 1.4′
; 1 pixel= 0′′
.08) divided into four channels of
1024 × 512 pixels each. Nube was observed on 9 and 10 January
2019. We followed the dithering strategy described in Trujillo
& Fliri (2016) to reduce as much as possible the scattered light
from the telescope structure.
The data reduction of the Nube images follows the steps de-
tailed in Montes et al. (2020) and briefly described here. The
entire reduction process was carried out in a controlled and en-
closed environment as described in Akhlaghi et al. (2021). After
the standard calibration per CCD channel (bias and flat field),
each set of four channels was assembled into a single image.
The different exposures that went into the final images were visu-
ally inspected, and those with low quality (too noisy and/or very
bright background) or strong gradients were discarded. Photo-
metric calibration of these images was performed using SDSS
DR12 (Alam et al. 2015). The size of Nube on the sky (effec-
tive diameter of ∼27′′
; see Fig. 1) is significantly smaller than
the FOV of the camera (162′′
× 84′′
), allowing reliable back-
ground subtraction and study of the galaxy using these images.
The background subtraction was performed by subtracting a cal-
culated constant value from the masked image. In addition to
masking the foreground and background sources, we masked
a circular region with a radius of 40′′
centred on Nube (that is
∼ 3Re of this galaxy, see Sec. 3.1) to avoid over-subtracting the
light associated with the outer parts of the galaxy.
The final exposure time on-source is 1 hour and 8 minutes
for each band. The limiting surface brightness depths of the final
images measured in 10′′
× 10′′
boxes are 30.5, 31, 30.5, 30 and
29.2 mag/arcsec2
for u, g, r, i and z (3σ above the background)
respectively, measured using the method described in Appendix
A of Román et al. (2020). The limiting magnitudes for point-like
sources are: 26.2, 26.7, 26.2, 25.8 and 25 mag from u to z (5σ
within an aperture of 2′′
).
2.2. GBT HI data
We performed ∼12 hours of observations with the Green Bank
Telescope (GBT)2
along the line of sight (LOS) to Nube be-
tween January 2019 and July 2019 (programmes GBT18B-356
and GBT19A-485). Our observational configuration is identical
to that of Karunakaran et al. (2020b), where we used the L-
band receiver and the VErsatile GBT Astronomical Spectrom-
eter (VEGAS) in Mode 7 (spectral resolution = 3 kHz ∼ 0.7
km/s, bandpass = 100 MHz). The use of such a wide bandpass,
sensitive out to recession velocities of ∼ 14000 km/s, is essential
in the blind search for HI in such a faint object, which can be at
any distance along the LOS.
These data were reduced using the standard GBTIDL3
pro-
cedure getps. We removed both narrowband and broadband Ra-
dio Frequency Interference (RFI) before searching for potential
HI signals. We note that broadband RFI (i.e. GPS L3, µ1.381
GHz) was particularly prominent, resulting in almost a third of
the data being flagged. The effective integration time of the final
2
The Green Bank Observatory is a facility of the National Science
Foundation operated under cooperative agreement by Associated Uni-
versities, Inc.
3
http://gbtidl.nrao.edu/
Article number, page 2 of 16
3. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
UGC 928
8248 ± 3 km/s
UGC 931
2001 ± 3 km/s
J012329.27-003157.1
8248 ± 3 km/s
J012323.04-003439.7
8355 ± 4 km/s
Nube
7480 ± 8
km/s
Fig. 1. SDSS RGB image of the 20′
×20′
region around Nube. The insets show a zoom in on the galaxy, showing how it appears on images with
different limiting surface brightness in the r-band (26.7, 28.6 and 30.5 mag/arcsec2
; 3σ on 10′′
×10′′
boxes). Previously known galaxies in the field
of view are labelled.
calibrated spectrum is therefore ∼8.5 hours. We also note that
the fluxes are scaled up by a factor of 20% due to the systematic
offset in the GBT noise diode calibration values (Goddy et al.
2020). We smoothed the resulting RFI-free spectrum at various
spectral resolutions to search for possible HI emission. Fig. 2
shows a faint HI detection at VHelio = 7480 ± 8 km/s (red line)
with a signal-to-noise ratio of 6.1, along with the statistically
independent XX and YY polarizations (blue and green lines, re-
spectively) that were co-added to produce the total spectrum. Al-
though faint, the line is detected in both XX and YY, and it is
also consistently detected in jackknifes about other observables
such as observing date and time. For a number of reasons, which
we explain below, we believe that this detection is most likely
associated with Nube.
We estimate the systemic heliocentric velocity (VHelio) and
velocity width (W50) of the HI detection using the methods de-
scribed in Karunakaran et al. (2020a,b), which are based on those
of Springob et al. (2005). Briefly, we fit first order polynomials
to each edge of the HI profile between 15% and 85% of the peak
flux and find the velocities corresponding to the 50% flux value.
The mean and difference of these velocities give VHelio and W50
respectively. We correct W50 for instrumental and cosmological
redshift broadening according to Springob et al. (2005) and for
ISM turbulence according to Verheijen & Sancisi (2001) (see
their section 4; see also Karunakaran et al. 2020b).
We convert VHelio to a kinematic distance (D) using the
Hubble-Lemaître law and assuming an uncertainty of 5 Mpc
due to peculiar velocities. The derived distance is 107 ± 5 Mpc.
We measure the HI flux (S HI) by integrating over the line pro-
file whose uncertainties are dominated by the noise and the
2% diode uncertainty (van Zee et al. 1997). The flux value is
S HI = 0.083 ± 0.02 Jy km/s. We use the kinematic distance to-
gether with the integrated flux in the standard equation for an
optically thin gas (Haynes & Giovanelli 1984) to calculate the
HI mass:
MHI = 2.356 × 105
D2
S HI [M⊙] (1)
resulting in MHI = 2.2+0.7
−0.5 × 108
M⊙. All derived properties from
the HI spectrum are at a spectral resolution of 25 km/s and are
listed in Table 1.
2.3. Possible sources of contamination in HI
Although it is tempting to associate the HI detection with the
Nube galaxy, it could be that the measurement corresponds to
another galaxy in the line of sight. For this reason, a detailed
analysis of the velocity distributions of the galaxies in the Nube
region is needed to see if the HI detection is compatible with any
of them.
Article number, page 3 of 16
4. A&A proofs: manuscript no. dgs82
6750 7000 7250 7500 7750 8000 8250
VHelio(km/s)
−0.75
−0.50
−0.25
0.00
0.25
0.50
0.75
1.00
1.25
Flux
(mJy)
Total
XX Pol.
YY Pol.
Fig. 2. HI detection along the line of sight to Nube. We also show differ-
ent polarisations of the data, XX and YY, to better identify which other
HI emission peaks in the spectrum are potentially spurious. The black
tick indicates the location of the peak with the strongest signal in our
data. Note that other distinct peaks are not always present in the two
different polarisations, thus reducing their relevance as real signals.
Using NED4
we have created a catalogue of all objects
in this database with spectroscopic redshifts in a region cen-
tred around Nube of 100′
× 100′
. The total number of galaxies
found is 711. All galaxies with recession velocities in the range
5480<Vhelio<9480 km/s, 42 galaxies, are plotted in Fig. 3. The
galaxies are colour coded according to the relative velocity of the
HI detection. In this region, there are many galaxies with relative
velocities ∆V<-600 km/s from the HI detection (red symbols in
the figure). There is also a smaller group with velocities about
500 km/s greater than the HI detection (purple symbols close to
the centre). Interestingly, there is no galaxy with known spec-
troscopic redshift within a radius of 10′
centred on Nube that
has a |∆V| < 500 km/s. This is important because this is the re-
gion where potential contamination from a gas-rich source could
mimic the signal we identify as possibly coming from Nube. To
better illustrate this point, in Fig. 3 we also show the 2D GBT
beam response using the well-characterised pattern at 1.4 GHz
from Spekkens et al. (2013). The contours (from blue to black)
indicate where the beam efficiency drops by the factor indicated
on the label.
The closest galaxy in terms of velocity (∆V = −17.8 km/s)
would be the spiral galaxy to the north: UGC929, in yellow in
Fig. 3. This galaxy is 14.7 arcmin or 435 kpc away at the distance
corresponding to the HI detection (i.e., 107 Mpc). This object is
close to the first minimum of the beam response, shown by the
grey-scale background image in Fig. 3, which means that the HI
emission, if coming, from UGC929 would be suppressed by a
factor of ∼104
. If the source of the HI emission is UGC929, this
implies that the HI mass of this galaxy should be ∼1012
M⊙. Us-
ing scaling relations between stellar mass and HI mass, a galaxy
with the stellar mass of UGC 929 (M∗ = 2.4 × 1010
M⊙, see Ap-
pendix A) is expected to have a mass in HI of ∼ 2 × 109
M⊙ and
no more than ∼ 2×1010
M⊙ (Feldmann 2020). This is at least 100
times less gas than what it is needed to reproduce the observa-
tions. It is, therefore, very unlikely that the emission we see at the
location of Nube is caused by the contamination from UGC929.
4
The NASA/IPAC Extragalactic Database (NED) is operated by the
Jet Propulsion Laboratory, California Institute of Technology, under
contract with the National Aeronautics and Space Administration
To the northwest in Fig. 3, there is another galaxy at a similar
velocity (∆V = −27.8 km/s) at 14′
away. This galaxy appears to
be a low-mass galaxy, probably a satellite of UGC929. Given it
is also located in the first minimum of the beam response and its
low mass, it is also very unlikely that it is the source of the HI
emission.
None of the galaxies with a confirmed spectroscopic redshift
appear to be responsible for the detection of HI in the Nube re-
gion. However, it is possible that the HI emission is coming from
a low-mass galaxy in the region which, due to its faintness, has
no spectroscopic redshift. To investigate this, we have made a
catalogue of all sources with a photometric redshift within a ra-
dius of 10′
around Nube. This radius corresponds to the area
where the response efficiency of the GBT beam is greater than
5% (see Fig. 3). We used one of the value added catalogues from
the DR9 DECaLS survey, which provides photometric redshifts
of sources down to a 5σ depth of mr = 24 mag (Zhou et al.
2021). The list of objects with a photometric redshift compatible
with the HI emission (i.e., z=0.02502) is given in Table C.1. The
vast majority of objects with a photometric redshift compatible
with the HI detection reported in this work are either a star or
a point-like source. This is somewhat to be expected, since at a
given magnitude photometric catalogues are biased towards ob-
jects with higher signal-to-noise, and therefore extended objects
are less represented or missing.
Finally, to account for the possibility that some faint and
diffuse galaxies might not have a photometric redshift mea-
sured, we visually inspected the inner 10′
around Nube using the
Dark Energy Camera Legacy Survey (DECaLS, Dey et al. 2019)
DR10 images to find extended faint sources that could poten-
tially be emitting in HI. We found only two very faint galaxies,
which are listed in Table C.2. These two galaxies are visually
smaller than Nube and therefore potentially less massive at the
same distance. Furthermore, these objects are found at a radial
distance of ≳ 4.5′
from the central direction of the HI beam.
While we cannot completely rule out the possibility that one of
these galaxies is responsible for the HI detection, their off-centre
location would imply that they are less likely to be associated
with the HI detection than Nube.
The analysis in this section reinforces the idea that the de-
tection of an emission peak in HI could be related to the opti-
cal detection of Nube. Moreover, the fact that the HI emission
observed coincides with the velocity of UGC929 (even if it is
extremely unlikely to be caused by it) is a further argument in
favour of the HI detection being genuine and not a fluctuation.
Having ruled out contamination of nearby HI sources, there is
still the possibility that the optical and HI detections are unre-
lated, and therefore the distance assumed for the optical coun-
terpart of the galaxy may be incorrect. However, this possibility
does come with its own problems. For a detailed discussion of
the implications of the distance for Nube, see the Appendix B.
The scenario that follows from the analysis in this section is that
Nube could be a satellite of UGC929, at a distance of 107 Mpc.
3. Analysis and results
3.1. Radial profiles of Nube
The aim of this paper is to study the properties of Nube in
detail in order to determine its origin. A fundamental way to
characterise the shape of a galaxy is through its radial surface
brightness profiles. In addition, multi-wavelength information
provides valuable constraints on galaxy formation processes.
We have, therefore, derived the surface brightness radial profiles
Article number, page 4 of 16
5. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
40 20 0 20 40
RA (arcmin)
40
20
0
20
40
DEC
(arcmin)
0.05%
0
.0
5
%
0
.
0
5
%
0.5%
5%
50%
600
400
200
0
200
400
600
V
(km/s)
-1 0 +1
R (Mpc)
Fig. 3. Galaxies found in NED with known spectroscopic redshifts in a range of 100′
× 100′
around Nube and a recession velocity within 2000
km/s of that of the HI detection (i.e. Vhelio = 7480 km/s). The galaxies are colour-coded according to their relative velocity with respect to the
potential velocity of Nube. The grey-scale background image is the GBT beam response from Spekkens et al. (2013). The contours indicate where
the efficiency drops by the factor indicated on the label, from 0.05% (black) to 50% (light blue). The top horizontal axis indicates the equivalent
size in Mpc at a distance of 107 Mpc.
of this galaxy using the optical, multi-wavelength, HiPERCAM
data.
To measure the photometry of this galaxy, we first masked
out all foreground and background sources in the image. As can
be seen in the insets in Fig. 1, the galaxy is very faint and al-
most transparent. Since we cannot determine whether the clumps
on top of the galaxy are part of the galaxy or are objects in the
line of sight of the galaxy, we masked them all, leaving only the
diffuse component for photometry. We used a combination of
NoiseChisel (Akhlaghi & Ichikawa 2015; Akhlaghi 2019) and
manual masking after visual inspection. This is a very conser-
vative approach as we are only analysing the diffuse light of the
galaxy. Appendix D shows the mask used in this work.
Once we had masked out all the sources of contamination,
we derived the radial surface brightness profiles of the galaxy.
Given the nearly circular shape of the object, we decided to ex-
tract the radial profiles using circular annuli at different radial
distances, up to 30′′
from the centre of the galaxy. To derive the
profiles, we use a custom python code. For each radial bin, the
surface brightness was obtained as the 3σ-clipped median of the
pixel values. Fig. 4 shows the surface brightness profiles of Nube
for the 5 bands imaged with HiPERCAM. Some of the profiles
are shifted by a constant value, given in the legend, for ease of
viewing. The errors are calculated as a combination of the Pois-
son noise in each annulus and the error in the sky given by the
distribution of background pixels in each image. These surface
brightness profiles are corrected for the absorption of our Galaxy
(E(B−V) = 0.34, Schlafly & Finkbeiner 2011).
We can now study the radial variations of the galaxy’s stel-
lar populations. The surface brightness profiles are used to de-
termine the radial g − r profile of the galaxy. The top panel in
Figure 5 shows the g − r colour profile of Nube. The colour pro-
file appears flat at all radii, with an average colour of ∼0.6. This
almost flat colour profile could be compatible with a similar age
and metallicity at all radii, up to 10′′
(15 kpc).
The bottom panel of Fig. 5 shows the surface stellar mass
density profile for this galaxy. To derive it, we follow the pro-
cedure given in Bakos et al. (2008) to link the observed sur-
face brightness in the g-band to the radial variation of the stellar
mass to light (M/L) ratio. The M/L ratio was obtained from the
prescriptions given in Roediger & Courteau (2015) assuming a
Chabrier (2003) IMF, using the g − r colour profile. As with the
Article number, page 5 of 16
6. A&A proofs: manuscript no. dgs82
0 5 10 15 20 25 30
Radius (arcsec)
24
25
26
27
28
29
30
31
Surface
Brightness
(mag/arcsec
2
)
u-band +0
g-band +0
r-band +0
i-band −0.5
z-band −1
Fig. 4. Radial surface brightness profiles of Nube in the Sloan u, g, r, i
and z bands. The profiles in the i and z bands have been shifted vertically
for ease of visualization.
colour profile, the stellar mass density profile of Nube is also
relatively flat compared to the stellar mass density profiles of
galaxies with similar stellar masses (e.g., Montes et al. 2021).
We expand on this result later in the text.
We have used this stellar mass density profile to measure the
radius that encloses half the mass of the galaxy, or the half-mass
radius (Re). This radius is Re = 13.7±1.7 arcsec (6.9±0.8 kpc at
a distance of 107 Mpc). The effective surface stellar mass density
of Nube is < Σ >e= 0.9 ± 0.1 M⊙ pc−2
. The total stellar mass of
the galaxy derived from the surface mass density profile, assum-
ing circular symmetry, is M∗ = 3.9±1.0×108
M⊙. The effective
surface brightness is < µV >e= 26.75 ± 0.02 mag/arcsec2
. These
values, along with other global properties of Nube, are listed in
the Table 1.
To assess the validity of our results, we also fitted Sérsic
(1968) models (using the code GALFIT Peng et al. 2002) to
the galaxy in all the different HiPERCAM bands, independently.
The values of the half-light effective radius, re, and the Sérsic in-
dex for each band are given in Table 2. The values of re from the
GALFIT fits are consistent with those derived using the surface
brightness profiles.
3.2. Stellar populations of Nube
Given the very low surface brightness of this galaxy (µV(0)∼26.2
mag/arcsec2
), the use of deep multi-wavelength observations is
the best, if not the only, way to constrain its stellar populations,
namely the age, metallicity and stellar mass-to-light ratio (M/L).
To estimate these quantities, we first constructed the spectral en-
ergy distribution (SED) of the galaxy (see Fig. 6). The photom-
etry at each band was derived measuring the total flux within
a circular aperture with radius equal to the half-mass radius Re
(13.7′′
) of the galaxy. The purpose of using this aperture (instead
of the total galaxy) is to ensure enough signal to reliably char-
acterise the SED of Nube. The errors of the photometry of each
individual band that compose the SED are a combination of the
photometric errors and the zero point uncertainties.
To characterise the stellar population properties of the
galaxy, we fitted Bruzual & Charlot (2003) single stellar popula-
tion (SSP, instantaneous burst) models to the SED of the galaxy.
0.3
0.4
0.5
0.6
0.7
0.8
(g
−
r)
0
0 10 20 30
Radius (arcsec)
0.01
0.10
1.00
Σ
(M
⊙
pc
−2
)
0 5 10 15
Radius (kpc)
Fig. 5. Upper panel: the HiPERCAM g − r colour profile of Nube. Bot-
tom panel: Stellar surface mass density profile of Nube. The upper hori-
zontal axis indicates the equivalent size in kpc at a distance of 107 Mpc.
This is a reasonable assumption given the homogeneous colour
distribution of this galaxy (Fig. 5). The parameters to be fit-
ted are three: age, metallicity and luminosity, and we assumed
a Chabrier Initial Mass Function (IMF, Chabrier 2003) for the
models. Since the SED is derived from broadband imaging, it is
a good approach to assume an SSP to describe the stellar pop-
ulations of this galaxy, since the information we have is lim-
ited. This assumption will give us the average properties of this
galaxy. For the fit, we use the χ2
minimisation approach de-
scribed in Montes et al. (2014). We derive a most likely age
of 10.2+2.0
−2.5 Gyr and a metallicity [Fe/H] of −1.09+0.09
−0.13, values
in agreement with those of old diffuse low-mass galaxies (see
e.g., Ruiz-Lara et al. 2018; Heesters et al. 2023; Iodice et al.
2023). Uncertainties in the parameters have been estimated by
marginalising the 1D probability distribution functions obtained
during the fitting. Since the colour profile of this galaxy is flat
at all radii (see Fig. 5), we assume that the stellar populations
obtained for the inner Re are representative for the whole galaxy.
Using the M/L derived from the SED fit ((M/L)V = 1.8+0.3
−0.5)5
,
the total stellar mass of Nube is M∗ = 4.4±0.8×108
M⊙, in agree-
ment with the stellar mass estimate derived in Sec. 3.1. As this
stellar mass is derived with the properties inside Re, we prefer to
use the previous estimate (Sec. 3.1) as it is more representative
of the whole galaxy.
5
This M/L value is consistent with the M/L ratios derived at each ra-
dial distance using the g − r colour profile in Sec. 3.1; a median of 1.7.
Article number, page 6 of 16
7. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
RA DEC z Distance log(MHI/M⊙) log(M∗/M⊙) Re µV(0)
(Mpc) (arcsec) (mag/arcsec2
)
01h
23m
27.37s
-00d
37′
27.83′′
0.02502±0.00003 107 ± 5 8.35 ± 0.12 8.6 ± 0.1 13.7 ± 1.7 26.23 ± 0.07
W50 < µV >e < Σ >e Age [Fe/H] b/a Re
km/s (mag/arcsec2
) (M⊙pc−2
) (Gyr) (kpc)
34 ± 11 26.75 ± 0.02 0.9 ± 0.1 10.2+2.0
−2.5 −1.09+0.09
−0.13 0.97±0.01 6.9 ± 0.8
Table 1. Global properties of Nube. The distance-dependent parameters have been calculated assuming that the object is at a distance of 107 Mpc.
0.3 0.4 0.5 0.6 0.7 0.8 0.9
¸ (¹m)
19.0
19.5
20.0
20.5
21.0
21.5
22.0
m
AB
(<
R
e
)
Age = 10:2+2:0
¡2:5 Gyr
[Fe/H] = ¡1:09+0:09
¡0:13
(M/L)V = 1.84+0:34
¡0:46 ¨¯
Fig. 6. Spectral energy distribution (SED, filled circles) of Nube derived
from HiPERCAM photometry within the half-mass radius. The best-fit
single stellar population model is shown as the blue line and the best-
fit magnitudes (model convolved with the filter response) are the open
circles. The age, metallicity and mass-to-light ratio corresponding to the
best fit model are given in the figure.
3.3. Dynamical mass of Nube
A rough estimate of the dynamical mass of this galaxy6
can
be obtained using the following equation from Spekkens &
Karunakaran (2018):
M3Re
dyn = 6.96 × 105
Re
W50
2 × sin(i)
!2
[M⊙] (2)
with Re the half-mass radius in kpc, i the inclination of the
HI disc in degrees, and W50 the turbulence-corrected velocity
width of the HI line. We calculate the inclination of the HI disc
as follows:
cos(i) = (b/a) (3)
In Table 1, we provide the axis ratio, b/a, of Nube obtained
from GALFIT Sérsic fits to the object (see sec. 3.1). The result-
ing value (0.97±0.01) is the average from the axis ratio measured
in the g, r, and i bands. That results in an inclination value of
6
This calculation assumes that Nube is in dynamical equilibrium. This
is a reasonable assumption given the large distance to its potential pro-
genitor UGC929.
13±3 deg. It is worth emphasizing that using the axis ratio of the
stellar distribution to characterise the inclination of the HI disc is
a rough approximation. The dynamical mass we derive for Nube
is 2.6 ± 1.7 × 1010
M⊙ within 3Re = 20.7 kpc.
3.4. A search for Globular Clusters
Globular clusters (GCs) provide a complementary way to esti-
mate the distance to an extragalactic object based on the univer-
sality of their luminosity function. The peak of the GC distri-
bution lies at MV = −7.6 mag for different galaxies (see e.g.,
Rejkuba 2012), making it a secondary distance indicator. There-
fore, the detection of GCs in Nube would help us to validate the
distance obtained with the HI detection. Note that the peak of the
GC luminosity at the distance of 107 Mpc (i.e., a distance modu-
lus of 35.15 mag) is expected at mg ≃ 27.5 mag, fainter than our
point-like 5σ limiting magnitudes meaning that it would be dif-
ficult to detect GCs, if any, in our images (see section 2.1). We
expect that an ultra-diffuse galaxy of similar stellar mass than
Nube would have around ∼10 GCs, although the range varies
from 0 to 30 GCs. However, only the brightest GCs of the sys-
tem are expected to be detectable.
We follow a similar procedure to detect globular clusters as
in Montes et al. (2020, 2021). In short, we first preselect the GCs
based on their morphology (size and ellipticity), and then we
refine the selection based on their colours. However, in this case
we do not have the high spatial resolution of the HST images
to make a preselection based on the morphology of the GCs,
but only the ground-based images. For this reason, we have to
impose very strict shape criteria to minimise contamination in
our selection.
We run SExtractor on our images in dual mode, with
the r-band image as the detection image. At a distance of 107
Mpc, globular clusters will look like point sources in the im-
ages. Therefore, to pre-select the GC candidates, we first select
stars in our images by imposing that the stellarity parameter in
SExtractor (‘CLASS_STAR’) is greater than 0.98. We do this
to estimate the FWHM of a point-like source in our images, to
impose strict conditions on our detections and to minimise con-
tamination from other objects. We find 6 point-like objects, 3
of which were detected in Gaia DR3 (Gaia Collaboration et al.
2023). The FWHM of these point-like objects are between 10
and 14 pixels (0.8′′
to 1.12′′
) and their ellipticities are < 0.1.
Therefore, based on these values, we pre-selected the GC candi-
dates with: ellipticity < 0.1, 9 < FWHM < 15 pix and mr < 26.2
mag, in order to minimise false detections.
After this initial selection, we also applied the (u−r)−(r−z)
colour-colour selection used in Taylor et al. (2017) to narrow
down the selection of GCs7
. To do this, we defined a colour-
colour region based on the position on the diagram of candidate
7
See Muñoz et al. (2014); Lim et al. (2020); Cantiello et al. (2020) for
other examples on using colour-colour diagrams to identify candidate
GCs.
Article number, page 7 of 16
8. A&A proofs: manuscript no. dgs82
0 2 4
u − r
−0.5
0.0
0.5
1.0
1.5
2.0
2.5
r
−
z
Fig. 7. The (u − r) − (r − z) colour-colour diagram of the initial sample
of GC candidates (blue) of Nube. The green squares are the location of
NGC5128 candidates in Taylor et al. (2017) with a probability greater
than 95% of being true GCs. The black dashed line indicates the convex
hull (envelope) computed as the smallest region containing all the green
squares.
GCs with a probability of >0.95 of being true GCs in Taylor
et al. (2017), the green squares in Fig. 7. To define this region, we
computed the convex hull or convex envelope, i.e., the minimum
region containing all GCs from Taylor et al. (2017) (dashed line
in Fig. 7).
Only two sources fall on the area defined by the GCs pro-
vided by Taylor et al. (2017)8
. However, both are very far from
Nube (>110′′
or 54 kpc from its centre), so they are unlikely to
be associated with the galaxy. We also checked the three sources
near the bottom of the region (u-r∼2, r-z∼0.25), but they are also
not spatially associated with Nube. In summary, we are unable to
detect any GCs associated with Nube, as expected, considering
both our point-like limiting magnitudes and if the distance to the
galaxy is 107 Mpc.
4. On the formation mechanism of Nube
4.1. Nube in comparison with other Low Surface Brightness
galaxies
The galaxy reported in this paper, Nube, has some extreme prop-
erties in terms of size and surface brightness. Fig. 8 shows the
structural properties of Nube compared to other low surface
brightness or dwarf galaxies compiled from the literature. The
grey open circles represent low-mass Local Group galaxies from
McConnachie (2012), the green open squares are field dwarfs,
while the orange crosses are satellite dwarfs (orbiting a more
8
Taylor et al. (2017) use the GCs of NGC5128 to generate their cat-
alogue. NGC5128 is a massive galaxy with intense merger activity.
Therefore, the population of GCs in this massive galaxy includes GCs
of a wide variety of origins, from those formed in-situ in this massive
galaxy to those accreted by mergers with a large number of dwarfs. In
this sense, the Taylor et al. (2017) catalogue is expected to contain a
very heterogeneous and complete sample of GCs.
massive galaxy) from Carlsten et al. (2021), pink ‘x’ are UDGs
in Coma from van Dokkum et al. (2015), the golden star is
UDG32 from Iodice et al. (2021) and the red diamonds are two
of the LSB galaxies in Virgo from Mihos et al. (2015). Com-
pared to all these objects, Nube appears quite unique due to its
low central surface brightness and extension for a galaxy of its
stellar mass. The closest objects in size, mass and central surface
brightness are the two LSB galaxies in Virgo from Mihos et al.
(2015): VLSB-B and VLSB-C9
and UDG32 in Hydra I (Iodice
et al. 2021). We do not include VLSB-A, as this LSB galaxy
is clearly tidally perturbed, as indicated by its visible tidal tails.
VLSB-C appears to be quite similar in size and brightness to
Nube (Re = 5.5 kpc and µV(0) = 26.7 mag/arcsec2
, Mihos et al.
2015). This galaxy shows no obvious signs of tidal stripping;
possibly it is an LSB galaxy in the cluster outskirts or falling
into the Virgo cluster for the first time.
We also compare Nube with other galaxies that have been
described as “almost dark" in previous works. One example
is AGC229385 (also known as Coma P.; Janowiecki et al.
2015; Brunker et al. 2019). Unlike Nube, this galaxy ap-
pears elongated. It also has an extreme ratio of HI to stellar
mass (MHI/M∗=81; Brunker et al. 2019) compared to Nube
(MHI/M∗ ∼ 1). This is also the case of AGC229101 (Leisman
et al. 2021). This galaxy is an HI source (MHI/M∗=98) with a
very dim optical counterpart (µg(0) = 26.6 mag/arcsec2
) and
Re = 3 kpc. Other two extended “almost dark" galaxies are
AGC229398 and AGC333576 (Gray et al. 2023). Their effec-
tive radii are large, 9 and 4.4 kpc respectively, and their stellar
masses (∼108
M⊙) are also close to Nube. However, their central
surface brightness are significantly brighter than Nube (23.8 and
24.6 mag/arcsec2
).
In addition to comparing the global properties of Nube with
other low-mass galaxies, it is also very instructive to compare its
surface mass density profile with respect to galaxies of similar
stellar mass. In Fig. 9, we show the stellar surface mass density
of Nube (blue dots) derived from the g − r colours (Sec. 3.1).
For comparison, we plot the profiles of dwarf galaxies of simi-
lar stellar mass (grey lines), in the mass range 1 − 5 × 108
M⊙
from Chamba et al. (2020). This shows how different Nube is
from typical dwarf galaxies of similar mass. Even ultra-diffuse
galaxies with large effective radius are not comparable to this
galaxy. For example, the iconic ultra-diffuse galaxy Dragonfly
44 (DF44), also shown as the green squares in Fig. 9, has a
re = 4.3 ± 0.2 kpc (van Dokkum et al. 2016)10
, and a central
surface brightness of µg(0) = 24.5 mag/arcsec2
. This is 1.5 times
smaller and 1.4 mag/arcsec2
brighter than Nube.
4.2. On the nature of Nube
Given the extreme properties of Nube, it is interesting to discuss
whether these properties are a result of the original formation
of this galaxy, or whether they are due to a later evolutionary
process caused by the environment in which it is found. In this
section, we discuss two possible alternatives. In the first, we ex-
plore whether Nube can be considered a tidal dwarf galaxy. The
second is whether Nube was born with a stellar density typical of
dwarf galaxies of the same stellar mass and has been deformed
by the environment into this peculiar structure. Either of these
9
To derive the mass of VLSB-C, we assume a B−V = 0.7 mag for this
galaxy, which is typical for dwarf galaxies and the M/L colour relation
in Bell et al. (2003).
10
Other estimates for re for DF44 are re = 3.3 ± 0.3 kpc (Chamba et al.
2020) and 3.9 ± 0.7 kpc (Saifollahi et al. 2021).
Article number, page 8 of 16
9. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
18
20
22
24
26
28
30
μ
V
(0)
(mag/arcsec
2
)
1
Re (kpc)
0.1 1 10 100
M* × 106
M⊙
0
1
R
e
(kpc)
McConnachie+2012
Carlsten+2021 Field
Carlsten+2021 Satellites
Mihos+2015 (Virgo)
van Dokkum+2015 (Coma)
Iodice+2021 (Hydra I)
Nube
Fig. 8. Comparison of the structural properties of Nube with respect to other Local Group galaxies from McConnachie (2012, grey open circles),
dwarf galaxies in Carlsten et al. (2021, green open squares and orange crosses), UDGs in Virgo from Mihos et al. (2015, red diamonds), UDG32
in Hydra I from Iodice et al. (2021, golden star) and Coma from van Dokkum et al. (2015, pink x). Although the central surface brightness is
typical of other dwarf galaxies, the stellar mass and half-mass radius make Nube, at a distance of 107 Mpc, an extreme object, even more so than
the UDGs in Virgo and Coma.
two possibilities (if correct) should be able to explain the stellar
populations and the present morphology of Nube.
4.2.1. Is Nube a Tidal Dwarf Galaxy (TDG)?
There is a population of galaxies whose formation mechanisms
would not be associated with what is expected to be the main
channel of formation of galaxies, i.e., gravitational collapse of
gas within a dark matter halo. These galaxies are known as Tidal
Dwarf Galaxies (TDGs). They form from material torn away
from larger galaxies by tidal interactions or by harassment (e.g.,
Duc & Bournaud 2008) and, as a result of their formation, they
exhibit characteristics such as significant gas fractions, low dark
matter content, and metallicity higher than expected for dwarf
galaxies of similar mass (e.g., Duc 2012).
Around 95% of the known TDG galaxies are located at rel-
atively modest distances (∼20 kpc) from their potential progen-
itors (Kaviraj et al. 2012). However, Nube is very distant (435
kpc) from its likely progenitor UGC929. This large distance
from its possible parent should not be considered as a factor
against Nube being a TDG, since the selection of TDG galax-
ies usually requires a visible tidal tail and is therefore biased
towards newly formed objects. Some simulations suggest that if
the TDG is massive enough (M> 108
M⊙) and escapes the parent
galaxy with sufficient velocity, it could become self-gravitating
and avoid falling back into its progenitor system (Bournaud &
Duc 2006). However, it is unclear how long TDGs formed in this
way could survive without the protection of a massive dark mat-
ter halo, as both axisymmetric and non-axisymmetric instabili-
ties would eventually destroy the system (Sellwood & Sanders
2022). Assuming that these galaxies manage to survive, they are
expected to remain gas-rich and very faint. These old galaxies
are therefore good candidates to be identified as “almost dark"
galaxies (see e.g., Cannon et al. 2015; Janowiecki et al. 2015;
Leisman et al. 2017; Román et al. 2021).
The metallicity observed in Nube ([Fe/H] = −1.09+0.09
−0.13) is
similar to that of normal dwarf galaxies (e.g., McConnachie
2012). However, it is lower than expected for currently form-
ing TDGs (solar metallicity, e.g., Duc et al. 2000), i.e., more
metallic as it inherits the metallicity of the more massive par-
ent galaxies. Nonetheless, given the age of the galaxy (9 Gyr),
it could have formed from ancient spirals with less enriched gas
than the present ones (see e.g., Recchi et al. 2015). Therefore,
Article number, page 9 of 16
10. A&A proofs: manuscript no. dgs82
0 5 10 15
Radius (kpc)
0.1
1
10
100
Σ
(M
⊙
pc
−2
)
Chamba et al. 2020
DF44
Nube
Fig. 9. Surface stellar mass density profile of Nube (blue dots) compared
with other galaxies of similar stellar mass. The profiles of dwarf galax-
ies from Chamba et al. (2020) in the same mass range (1-5×108
M⊙)
have been plotted. We also show the profile of DF44 (green squares), as
it is an iconic large ultra-diffuse galaxy. The vertical lines indicate the
half-mass radius (Re) for Nube (blue solid line) and DF44 (green dashed
line).
the relatively low metallicity of Nube should not necessarily be
an indication that it did not form as a TDG.
Another characteristic of TDGs is their low dark matter
content. The dynamical mass of Nube is 2.6 ± 1.7 × 1010
M⊙
within 3Re = 20.7 kpc (Sec. 3.3), while the stellar mass is
M∗ = 3.9 ± 1.0 × 108
M⊙ (Sec. 3.2). This means that the ratio of
dark matter to stellar mass is between 20 − 150. This amount of
dark matter is significantly larger than the amount of dark mat-
ter expected if the galaxy had formed as a TDG (Mdyn/M∗ <2;
Gray et al. 2023). In addition, its gas content relative to the stel-
lar content is not very large compared to those found in other
TDGs (MHI/M∗ ∼10, Gray et al. 2023). For these reasons, we
conclude that Nube is with high confidence not a TDG.
4.2.2. Nube as a result of environmental processes
If Nube is not a TDG, can its structural properties be explained
as the result of interaction with its environment? It is known that
dwarf galaxies can be dynamically heated and “puffed up” by
interactions with more massive galaxies (e.g., Liao et al. 2019;
Tremmel et al. 2020). This puffing could explain why the age and
metallicity of Nube are similar to other regular dwarf galaxies,
while its physical properties (effective radius and central surface
brightness) are extreme. However, against this scenario for the
origin of Nube is the fact that the galaxy does not inhabit a partic-
ularly dense environment. In fact, its nearest massive neighbour,
UGC 929, is at a distance of 435 kpc in projection.
Assuming that Nube and UGC 929 have had a close en-
counter in the past, we can make a rough estimate of when this
occurred. Considering the current projected distance between the
two objects plus a transverse projected velocity of ∼100 km/s
(i.e., 100 kpc/Gyr), the close encounter would have occurred 4
to 5 Gyr ago. Given the dynamical time of each galaxy, this is
Fig. 10. A region of 100′′
×100′′
around Nube. The figure is a composite
of an RGB colour image using the g, r and i HiPERCAM bands and a
black and white g + r image for the background.
enough time to have erased any signature of the perturbation in
the central regions of both objects. We do not find the central re-
gion of Nube to be obviously perturbed (see Fig. 10). Regarding
UGC929, we have used deep imaging from DECaLS to study its
morphology. Fig. A.1 shows the composite DECaLS image of
the galaxy. We can see in the image that the galaxy appears to
be very symmetric, with no sign of perturbations or interactions.
Therefore, if Nube and UGC929 had met in the past, it would
have been long enough for the central shape of both galaxies to
have already been restored.
However, in the outermost parts of Nube it would be pos-
sible to study the effects of this gravitational interaction in the
form of tidal distortions. These deformations produce an S-
shaped structure (e.g. Johnston et al. 2002; Moreno et al. 2022).
Thanks to the deep imaging provided by HiPERCAM, we can
investigate whether there is any evidence that this could be the
case for Nube. An interaction capable of distorting the galaxy
in this way would be clearly visible in our ultra-deep imaging
(∼30.5 mag/arcsec2
; see Sec. 2.1) even long after the interaction
(Moreno et al. 2022). Fig. 10 shows an RGB composite of the
image of Nube with a black and white background to highlight
the fainter outskirts of this galaxy. A visual inspection of Nube
shows no obvious signatures of deformation in the outer regions.
This can be seen from the lack of an excess in the outer parts of
the surface brightness and stellar density profiles (Fig. 4 and Fig.
5), which is associated with the presence of tidal tails (Johnston
et al. 2002; Montes et al. 2020).
To improve the visualization of the outer parts of Nube, we
also modelled Nube with GALFIT. To obtain additional signal-
to-noise, we have performed a model fit on a g + r image. Fig.
11 shows the original (left), model (middle) and residual (right)
g + r image. No signs of an excess or deformation can be seen.
Article number, page 10 of 16
11. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
Fig. 11. GALFIT model of Nube for the HiPERCAM g + r-band. The left panel shows the g+r original image, the middle panel the 2-D Sérsic
model fit and the right panel the residuals after subtracting the Sérsic model, after smoothing it with a Gaussian kernel to enhance the residuals.
filter re n b/a
(arcsec)
u 15.6 ± 0.6 0.60 ± 0.03 0.999
g 15.9 ± 0.1 0.70 ± 0.01 0.986
r 15.3 ± 0.1 0.65 ± 0.01 0.962
i 13.9 ± 0.1 0.60 ± 0.01 0.975
z 16.0 ± 0.3 0.75 ± 0.02 0.971
Table 2. Multi-band effective radii, axis ration and Sérsic indexes of the GALFIT (Peng et al. 2002) fits to Nube.
5. Nube as a test-bed to explore the nature of dark
matter
5.1. Nube within the cold dark matter scenario
Given the extreme properties of Nube, it is interesting to see
whether traditional models of cold dark matter are able to re-
produce galaxies with these characteristics. In particular, we are
interested in knowing if galaxy formation models can produce
objects with stellar masses, surface brightnesses and effective
radii like Nube. To answer this question, it is worth looking at
simulations that have been able to reproduce the properties of the
largest known ultra-diffuse galaxies. These simulations have suf-
ficient spatial resolution and stellar population feedback recipes
to produce low surface brightness, large effective radius galaxies
like DF44.
Using the FIRE-2 simulations (Hopkins et al. 2018), Chan
et al. (2018) find that isolated field dwarfs, where the effect of
stellar feedback (i.e., stellar winds, supernovae, etc.) is large,
produce galaxies with surface brightness, effective radius, and
stellar masses representative of UDGs (after imposing artificial
quenching to simulate the effect of infall into the cluster envi-
ronment). Simulated galaxies with stellar masses around 108
M⊙
and dark matter halos around 1010
M⊙, such as Nube, have ef-
fective radii less than 5 kpc, smaller than what we measure for
Nube. NIHAO simulations (Wang et al. 2015) produce galaxies
with similar structural properties to UDGs due to episodes of gas
outflows associated with star formation (Di Cintio et al. 2017).
The dark matter halo masses and stellar masses are consistent
with what we find for Nube. However, the effective radii (∼3
kpc) of these simulated galaxies are again well below the value
we measure for Nube.
Other ways that have been proposed to form UDGs are high-
z major mergers (Wright et al. 2021) or that UDGs populate
higher spin halos (Amorisco & Loeb 2016; Benavides et al.
2023). However, neither of these scenarios can reproduce the
observed characteristics of Nube. In Wright et al. (2021), ma-
jor mergers produce galaxies with re < 4 kpc. Benavides et al.
(2023) explores UDGs in the TNG50 simulation and finds that
for isolated galaxies of the mass of Nube, the effective radius is
≲ 5 kpc.
5.2. Nube in the fuzzy dark matter framework
As the microphysical nature of the dark matter is still completely
unknown, it is worth exploring whether extreme objects such as
Nube can be compatible with other alternative dark matter mod-
els. In particular, models based on ultralight (axion-like) scalar
particles are gaining recently a significant interest (fuzzy dark
matter; Schive et al. 2014; May & Springel 2021). Due to the
very small mass of these particles (∼10−22
eV), the quantum ef-
fects are expected to appear at the kpc (i.e., galactic) scale. The
ultralight particles generate dark matter models with large cores.
In particular, the dark matter distribution is expected to generate
a central distribution named soliton followed by a NFW profile
in the outer parts (Schive et al. 2014). The soliton density profile
can be well approximated by:
ρs(r) =
1.9(mB/10−23
eV)−2
(rc/kpc)−4
[1 + 9.1 × 10−2(r/rc)2]8
M⊙ pc−3
(4)
with mB the mass of the dark matter particle, rc the core ra-
dius where the density has dropped to one-half its peak value.
Equation 29 of Bar et al. (2018) shows that if the core radius and
the virial mass of the dark matter halo Mh is known, the dark
matter particle can be estimated through the following equation:
mB
10−22eV
= 160
rc
pc
!−1
Mh
1012M⊙
!−1/3
(5)
Article number, page 11 of 16
12. A&A proofs: manuscript no. dgs82
To get a rough estimate of the core radius, we assume the
stellar distribution follows the shape of the dark matter soli-
ton. This is a reasonable assumption, as the dark matter is the
dominant component generating the global gravitational poten-
tial (Sánchez Almeida et al. 2023). Therefore, we project the
soliton density profile obtaining:
Σ⋆(R) =
Σ⋆(0)
(1 + 0.091 × (R/rc)2)15/2
(6)
The stellar mass surface density of Nube fits very well with
this equation (see Fig. 12). We obtain a value of rc = 6.6 ± 0.4
kpc. The mass of the dark matter particle compatible with this
core radius is mB=(0.8+0.4
−0.2)×10−23
eV.
We also plot a Navarro, Frenk & White profile (dashed black
line, Navarro et al. 1996) to show that this commonly used pro-
file to describe the distribution of mass in dark matter halos
cannot reproduce the characteristics of Nube especially at small
radii. For Fig. 12, we used the projected NFW profile in equation
11 in Wright & Brainerd (2000), assuming as transition radius
(rs) the core radius of the soliton derived above.
It is interesting to compare the mass of the axion-like par-
ticle derived in this analysis with other studies. Using galactic
rotation curves, Bernal et al. (2018) found an average value of
mB∼0.5×10−23
eV, while Bañares-Hernández et al. (2023) de-
rived mB∼2×10−23
eV. These values are in good agreement with
our estimate using only the structural properties of the galaxy.
Analysing the velocity dispersion of the Fornax and Sculptor
dwarfs, González-Morales et al. (2017) find an upper limit of
mB<4×10−23
eV. Based on the angular scale of the CMB acous-
tic peaks and anisotropies, Hložek et al. (2018) derive a lower
limit of mB>0.1×10−23
eV. Analysis of the stellar heating of the
Milky Way disc due to the substructure within a fuzzy dark mat-
ter halo suggests an upper limit of mB<4×10−23
eV (Chiang et al.
2023). These results are consistent with our estimate for the mass
of the axion-like particle.
However, the situation is far from clear. Other estimates of
the mass of the particle are inconsistent with the above results.
To name a few, Chen et al. (2017) using Jeans analysis of the
Milky Way satellite dSphs find mB=(17.9±3.3)×10−23
eV. Dalal
& Kravtsov (2022) suggest that the size and stellar kinematics
of ultra-faint dwarfs imply a lower limit of mB>3×10−19
eV. Al-
though fuzzy dark matter could relieve some of the small scale
tensions appearing in the cold dark matter scenario, more work
is needed to assess this model.
6. Conclusions
In the absence of a laboratory detection of the particles that
make up dark matter, the hope for characterising its nature lies in
the analysis of astrophysical objects. In particular, galaxies with
very low surface brightness (also called “almost dark”) offer an
interesting possibility to constrain the microphysical properties
of dark matter. In these galaxies, baryonic feedback effects are
expected to be very moderate, leaving the spatial distribution of
their dark matter halo almost intact.
In this paper, we present the serendipitous discovery in the
IAC Stripe 82 Legacy Project (Fliri & Trujillo 2016; Román &
Trujillo 2018) of a galaxy, Nube, of stellar mass M∗ = 3.9±1.0×
108
M⊙, very extended (Re = 6.9 ± 0.8 kpc) and very low sur-
face brightness (<µV>e= 26.75 ± 0.02 mag/arcsec2
) located at
107 Mpc. Using the GBT radio telescope, we inferred a total
halo mass of 2.6 ± 1.7 × 1010
M⊙ for the galaxy. Current simula-
tions of ultra-diffuse galaxy formation, which take into account
1 10
Radius (kpc)
0.1
1
5
Σ
*
(M
⊙
pc
−2
)
Fig. 12. Surface stellar mass density profile of Nube (blue dots) fitted
with a projected soliton shape with core radius of rc = 6.6 ± 0.4 kpc
(see text for details). The soliton best fit and its errors are indicated by
the red line and the red region. The agreement is remarkable taking into
account that the only free parameter is essentially the core radius. The
black dashed line is a projected NFW profile for comparison.
baryonic feedback effects and simulate dark matter particles as
WIMPs (i.e., cold dark matter), are unable to reproduce objects
with the properties of Nube. We have investigated the possibility
that the object could be reproduced with the predictions for the
fuzzy dark matter model. To this end, and under the hypothesis
that the distribution of stars in Nube is representative of the dis-
tribution of the dark matter halo, we found that a soliton-shaped
profile (typical of fuzzy dark matter) reproduces the observed
distribution of stars very well. The mass of the axion-like parti-
cle inferred from the fit is mB=(0.8+0.4
−0.2)×10−23
eV. This value is
in good agreement with other astrophysical measurements using
the dynamical properties of other low surface brightness galax-
ies.
Acknowledgements. We thank the referee for their useful comments that helped
improve the original manuscript. We are indebted to Amelia Trujillo González
for suggesting the name of the galaxy explored in this work. The authors want to
thank Scott Carlsten for providing the tables of the structural parameters of the
dwarf galaxies in Carlsten et al. (2021). We also thank Betsy Adams and Pierre-
Alain Duc for useful discussions. This publication is part of the Project PCI2021-
122072-2B, financed by MICIN/AEI/10.13039/501100011033, and the Euro-
pean Union “NextGenerationEU”/RTRP. I.T. acknowledges support 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 the State Research Agency (AEI-
MCINN) of the Spanish Ministry of Science and Innovation under the grant
PID2019-107427GB-C32, financed by the Ministry 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. MM and IT acknowledge support from IAC project P/302302. NC
acknowledges support from the research project grant ‘Understanding the Dy-
namic Universe’ funded by the Knut and Alice Wallenberg Foundation under Dnr
KAW 2018.0067. Based on observations made with the GTC telescope, in the
Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica
de Canarias, under Director’s Discretionary Time. This work makes use of the
following code: astropy (The Astropy Collaboration et al. 2018), SExtractor
(Bertin & Arnouts 1996), SCAMP (Bertin 2006), SWarp (Bertin 2010), Gnuastro
(Akhlaghi & Ichikawa 2015), photutils v0.7.2 (Bradley et al. 2019), pillow
(van Kemenade et al. 2020), numpy (Oliphant 2006), scipy (Virtanen et al.
2020), Astrometry.net (Lang et al. 2010), GALFIT (Peng et al. 2002).
Article number, page 12 of 16
13. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
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Article number, page 13 of 16
14. A&A proofs: manuscript no. dgs82
to Nube
Fig. A.1. A region of 250′′
× 250′′
(∼123 kpc × 123 kpc) around the
galaxy UGC929. The figure is a composite of an RGB image using
the g, r and z from DECaLS and a black and white g + r + z image
for the background. This galaxy is at the same redshift that Nube, but
14.7′
to the north-west. The blue arrow indicates the direction of Nube.
There is no evidence of morphological disturbance that could point to
gas expulsion as the origin of Nube.
Appendix A: Properties of UGC929
Given the difference in distance between both galaxies, we as-
sumed that Nube is a satellite of UGC 929. UGC 929 is at a pro-
jected distance of 14.7′
(435 kpc at a distance of 107 Mpc) from
Nube. To calculate the stellar mass of UGC929, we use the DE-
CaLS g and r images, obtaining the M/L ratio using the Roedi-
ger & Courteau (2015) prescriptions and assuming a Chabrier
(2003). The stellar mass of the galaxy is M∗ = 2.4 × 1010
M⊙.
Appendix B: Alternative distances to Nube
Some of the most peculiar properties of Nube depend on the as-
sumed distance to the galaxy. In Section 2.3 we found that it is
unlikely that another nearby galaxy could be responsible for the
HI emission we detected. However, we cannot completely rule
out the possibility that the HI detection is not related to Nube. In
that case, the galaxy could be at a different distance from the one
assumed in this work. For this reason, it is worth exploring what
alternative distances are potentially possible.
One possibility is that Nube is a satellite of a galaxy in the
field of view other than UGC929. Exploring the nearby galax-
ies with spectroscopic redshifts (Fig. 1), Nube could be associ-
ated with UGC928 (8248 km/s). However, if it is associated with
UGC928 (projected separation of ∼ 3.8′
), Nube will be even fur-
ther away and its properties will be even more extreme. Alter-
natively, Nube could be closer to us. In Fig. B.1 we show the
inferred properties of Nube at different distances, from 2 Mpc
(white) to the assumed distance of 107 Mpc (darker blue). The
only galaxy in the field of view with a spectroscopic redshift that
is closer to us is UGC931 (Fig. 1) at ∼ 30 Mpc (Springob et al.
2009). If Nube it is associated with UGC931, its properties will
also be peculiar. Its stellar mass and Re will be similar to those
of UDGs, but it would have a significantly lower central surface
brightness (3rd to 4th hexagon from the left, upper right panel in
Fig. B.1).
For Nube to be a more normal galaxy, the distance should be
between 2 and 10 Mpc. In this case, Nube will be more like the
low-mass Local Group galaxies of McConnachie (2012), such
as Phoenix (M∗ = 0.7 × 106
M⊙, re = 454 pc and µV(0) = 25.8
mag/arcsec2
) or the dwarfs of Carlsten et al. (2021). However,
there is no nearby massive galaxy to act as a host for Nube in
such case, and therefore it would be a rare example of an isolated
very low-mass galaxy.
Appendix C: Photometric redshifts and other
sources around Nube
Given the spatial resolution of the GBT data, in section 2.3 we
discussed the possibility that the HI detection corresponds to an-
other source and not to Nube. Table C.1 lists all galaxies with
photometric redshifts within 10′
of Nube. Table C.2 lists faint
sources that have neither spectroscopic nor photometric red-
shifts, but could be responsible for the HI emission.
Appendix D: Masks for photometry and surface
brightness profiles
Masking is a key component in obtaining reliable photometry
and surface brightness profiles of the galaxy under study. In sec-
tion 3.1 we describe how the HiPERCAM mask used to derive
the photometry and surface brightness profiles of Nubewas cre-
ated. Fig. D.1 shows the mask used to derive the photometry and
surface brightness profiles of the galaxy.
Article number, page 14 of 16
15. Mireia Montes et al.: An almost dark galaxy with the mass of the Small Magellanic Cloud
18
20
22
24
26
28
30
μ
V
(0)
(mag/arcsec
2
)
1
Re (kpc)
0.1 1 10 100
M* × 106
M⊙
0
1
R
e
(kpc)
McConnachie+2012
Carlsten+2021 Field
Carlsten+2021 Satellites
Mihos+2015 (Virgo)
van Dokkum+2015 (Coma)
Iodice+2021 (Hydra I)
Nube
Fig. B.1. Same as Fig. 8 but showing Nube at different distances 2, 10, 25, 50, 75 and 107 Mpc.
RA DEC z mr distance
(deg) (deg) (AB mag) (arcmin)
20.7455 -0.6473 0.028±0.03 17.3 7.3*
20.8104 -0.6972 0.025±0.03 20.4 5.5a
20.8105 -0.7059 0.025±0.02 21.0 5.9a
20.8349 -0.6543 0.025±0.1 20.3 2.5*
20.7561 -0.5262 0.027±0.05 17.2 8.9*
20.7682 -0.5045 0.026±0.2 20.2 9.2*
20.7984 -0.6008 0.025±0.1 20.6 4.2*
20.8535 -0.5496 0.026±0.1 20.0 4.5*
20.8571 -0.5475 0.025±0.01 12.1 4.6*
20.9294 -0.4799 0.026±0.09 20.4 9.5*
21.0163 -0.6003 0.027±0.15 20.5 9.2*
Table C.1. List of objects with photometric redshifts compatible with the HI detection reported in this paper. The vast majority of these objects
are stars or point-like sources (marked with *), another two sources (marked with a
) are part of a known galaxy, UGC931.
RA DEC Distance to Nube
(deg) (deg) (arcmin)
20.9390 -0.6132 4.5
20.9092 -0.5122 7.2
Table C.2. List of faint sources around Nube that we cannot exclude as responsible for the HI emission reported in this work.
Article number, page 15 of 16
16. A&A proofs: manuscript no. dgs82
Fig. D.1. Mask (blue regions) applied to a HiPERCAM RGB colour
(g+r+i) image of a region 100′′
× 100′′
around Nube. The black and
white background is a g + r image. The image shows the need for thor-
ough masking in these ultra-deep images.
Article number, page 16 of 16