Implications for galaxy formation models from observations of globular clusters around ultradiffuse galaxies

We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultradiffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii (Re), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, NGC by using sufficiently deep observations that (i) reach the turnover of the globular cluster luminosity function (GCLF) and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We find that NGC for these galaxies is on average ∼ 20, which implies an average total mass, Mtotal, ∼ 1011 M⊙ when applying the relation between NGC and Mtotal. This value of NGC lies at the upper end of the range observed for dwarf galaxies of the same stellar mass and is roughly a factor of two larger than the mean. The GCLF, radial profile, and average colour are more consistent with those observed for dwarf galaxies than with those observed for the more massive (L*) galaxies, while both the radial and azimuthal GC distributions closely follow those of the stars in the host galaxy. Finally, we discuss why our observations, specifically the GC number and GC distribution around these six UDGs, pose challenges for several of the currently favoured UDG formation models

The Fornax Cluster VLT Spectroscopic Survey: IV. Cold kinematical substructures in the Fornax core from COSTA

Context. Substructures in stellar haloes are a strong prediction of galaxy formation models in ΛCDM. Cold streams such as those from small satellite galaxies are extremely difficult to detect and kinematically characterize. The COld STream finder Algorithm (COSTA) is a novel algorithm able to find streams in the phase space of planetary nebulae (PNe) and globular cluster (GC) populations. COSTA isolates groups of (N) particles with small velocity dispersion (between 10 km s−1 and ∼120 km s−1) using an iterative (n) sigma-clipping over a defined number of (k) neighbor particles. Aims: We applied COSTA to a catalog of PNe and GCs from the Fornax Cluster VLT Spectroscopic Survey (FVSS) within ∼200 kpc from the cluster core in order to detect cold substructures and characterize their kinematics (mean velocity and velocity dispersion). Methods: We selected more than 2000 PNe and GCs from the FVSS catalogs and adopted a series of optimized setups of the COSTA parameters based on Montecarlo simulations of the PN and GC populations to search for realistic stream candidates. We find 13 cold substructures with velocity dispersion ranging from ∼20 to ∼100 km s−1, which are likely associated either to large galaxies or to ultra-compact dwarf (UCD) galaxies in the Fornax core. Results: The luminosities of these streams show a clear correlation with internal velocity dispersion, and their surface brightness correlates with their size and distance from the cluster center, which is compatible with the dissipative processes producing them. However, we cannot exclude that some of these substructures formed by violent relaxation of massive satellites that finally merged into the central galaxy. Among these substructures we have: (1) a stream connecting NGC 1387 to the central galaxy, NGC 1399, previously reported in the literature; (2) a new giant stream produced by the interaction of NGC 1382 with NGC 1380 and (possibly) NGC 1381; (3) a series of streams kinematically connected to nearby UCDs; and (4) clumps of tracers with no clear kinematical association to close cluster members. Conclusions: We show evidence for a variety of cold substructures predicted in simulations. Most of the streams are kinematically connected to UCDs, supporting the scenario that they can be remnants of disrupted dwarf systems. However, we also show the presence of long coherent substructures connecting cluster members and isolated clumps of tracers possibly left behind by their parent systems before these merged into the central galaxy. Unfortunately, the estimated low-surface brightness of these streams does not allow us to find their signatures in the current imaging data and deeper observations are needed to confirm them

Object classification with Convolutional Neural Networks: from KiDS to Euclid

Large-scale imaging surveys have grown about 1000 times faster than the number of astronomers in the last 3 decades. Using Artificial Intelligence instead of astronomer's brains for interpretative tasks allows astronomers to keep up with the data. We give a progress report on using Convolutional Neural Networks (CNNs) to classify three classes of rare objects (galaxy mergers, strong gravitational lenses and asteroids) in the Kilo-Degree Survey (KiDS) and the Euclid Survey

VizieR Online Data Catalog: Fornax galaxy cluster NIR images & catalogs (Saifollahi+, 2021)

We present optical and near-infrared photometry of sources in the Fornax cluster field in 6 filters (u, g, r, i, J and Ks), including catalogues of Globular Clusters (GCs) and Ultra-Compact Dwarfs (UCDs) in the Fornax Cluster. The optical and near-infrared images stem from three different data sets and cover 16 square degrees out to the virial radius of the Fornax cluster: the optical data of the Fornax Deep Survey (FDS) in u, g, r, i and near-infrared data from the VISTA Hemisphere Survey (VHS) in J and ESO/VISTA archival data in Ks. We also present the final coaaded Ks images of the Fornax galaxy Cluster. We used a deep set of Ks band observations of the Fornax cluster (ESO programme ID 090.B-0.477(A), 092.B-0.622(A), 094.B-0.536(A), 096.B-0.532(A), PI: Munoz) that were carried out using VIRCAM, the near-infrared camera of the VISTA telescope from October 2012 to March 2016. The final co-added frames have an average FWHM~0.7-arcsec and a 5σ limiting magnitude of 18.4mag (~1.0-arcsec and 17.7mag for the Ks data of VHS). (8 data files)

Quasar Candidates behind the Milky Way Disk and M31

Quasars behind the Milky Way, M31 and other nearby galaxies are useful for absorption line studies. Here we report spectroscopic follow-up of four quasar candidates behind the Galactic plane and two behind the Andromeda galaxy

The Fornax Cluster VLT Spectroscopic Survey. IV. Cold kinematical substructures in the Fornax core from COSTA

Context. Substructures in stellar haloes are a strong prediction of galaxy formation models in ΛCDM. Cold streams such as those from small satellite galaxies are extremely difficult to detect and kinematically characterize. The COld STream finder Algorithm (COSTA) is a novel algorithm able to find streams in the phase space of planetary nebulae (PNe) and globular cluster (GC) populations. COSTA isolates groups of (N) particles with small velocity dispersion (between 10 km s−1 and ∼120 km s−1) using an iterative (n) sigma-clipping over a defined number of (k) neighbor particles. Aims: We applied COSTA to a catalog of PNe and GCs from the Fornax Cluster VLT Spectroscopic Survey (FVSS) within ∼200 kpc from the cluster core in order to detect cold substructures and characterize their kinematics (mean velocity and velocity dispersion). Methods: We selected more than 2000 PNe and GCs from the FVSS catalogs and adopted a series of optimized setups of the COSTA parameters based on Montecarlo simulations of the PN and GC populations to search for realistic stream candidates. We find 13 cold substructures with velocity dispersion ranging from ∼20 to ∼100 km s−1, which are likely associated either to large galaxies or to ultra-compact dwarf (UCD) galaxies in the Fornax core. Results: The luminosities of these streams show a clear correlation with internal velocity dispersion, and their surface brightness correlates with their size and distance from the cluster center, which is compatible with the dissipative processes producing them. However, we cannot exclude that some of these substructures formed by violent relaxation of massive satellites that finally merged into the central galaxy. Among these substructures we have: (1) a stream connecting NGC 1387 to the central galaxy, NGC 1399, previously reported in the literature; (2) a new giant stream produced by the interaction of NGC 1382 with NGC 1380 and (possibly) NGC 1381; (3) a series of streams kinematically connected to nearby UCDs; and (4) clumps of tracers with no clear kinematical association to close cluster members. Conclusions: We show evidence for a variety of cold substructures predicted in simulations. Most of the streams are kinematically connected to UCDs, supporting the scenario that they can be remnants of disrupted dwarf systems. However, we also show the presence of long coherent substructures connecting cluster members and isolated clumps of tracers possibly left behind by their parent systems before these merged into the central galaxy. Unfortunately, the estimated low-surface brightness of these streams does not allow us to find their signatures in the current imaging data and deeper observations are needed to confirm them

Ultra-compact dwarfs beyond the centre of the Fornax galaxy cluster:hints of UCD formation in low-density environments

Abstract Ultra-compact dwarf galaxies (UCDs) were serendipitously discovered by spectroscopic surveys in the Fornax cluster 20 yr ago. Nowadays, it is commonly accepted that many bright UCDs are the nuclei of galaxies that have been stripped. However, this conclusion might be driven by biased samples of UCDs in high-density environments, on which most searches are based. With the deep optical images of the Fornax Deep Survey, combined with public near-infrared data, we revisit the UCD population of the Fornax cluster and search for UCD candidates, for the first time, systematically out to the virial radius of the galaxy cluster. Our search is complete down to magnitude mg = 21 mag or Mg∼ −10.5 mag at the distance of the Fornax cluster. The UCD candidates are identified and separated from foreground stars and background galaxies by their optical and near-infrared colours. This primarily utilizes the u−i/i−Ks diagram and a machine learning technique is employed to incorporate other colour combinations to reduce the number of contaminants. The newly identified candidates (44) in addition to the spectroscopically confirmed UCDs (61), increase the number of known Fornax UCD considerably (105). Almost all of the new UCD candidates are located outside the Fornax cluster core (360 kpc), where all of the known UCDs were found. The distribution of UCDs within the Fornax cluster shows that a population of UCDs may form in low-density environments. This most likely challenges the current models of UCD formation

The Fornax Cluster VLT Spectroscopic Survey

Context. Substructures in stellar haloes are a strong prediction of galaxy formation models in ΛCDM. Cold streams such as those from small satellite galaxies are extremely difficult to detect and kinematically characterize. The COld STream finder Algorithm (COSTA) is a novel algorithm able to find streams in the phase space of planetary nebulae (PNe) and globular cluster (GC) populations. COSTA isolates groups of (N) particles with small velocity dispersion (between 10 km s−1 and ∼120 km s−1) using an iterative (n) sigma-clipping over a defined number of (k) neighbor particles. Aims. We applied COSTA to a catalog of PNe and GCs from the Fornax Cluster VLT Spectroscopic Survey (FVSS) within ∼200 kpc from the cluster core in order to detect cold substructures and characterize their kinematics (mean velocity and velocity dispersion). Methods. We selected more than 2000 PNe and GCs from the FVSS catalogs and adopted a series of optimized setups of the COSTA parameters based on Montecarlo simulations of the PN and GC populations to search for realistic stream candidates. We find 13 cold substructures with velocity dispersion ranging from ∼20 to ∼100 km s−1, which are likely associated either to large galaxies or to ultra-compact dwarf (UCD) galaxies in the Fornax core. Results. The luminosities of these streams show a clear correlation with internal velocity dispersion, and their surface brightness correlates with their size and distance from the cluster center, which is compatible with the dissipative processes producing them. However, we cannot exclude that some of these substructures formed by violent relaxation of massive satellites that finally merged into the central galaxy. Among these substructures we have: (1) a stream connecting NGC 1387 to the central galaxy, NGC 1399, previously reported in the literature; (2) a new giant stream produced by the interaction of NGC 1382 with NGC 1380 and (possibly) NGC 1381; (3) a series of streams kinematically connected to nearby UCDs; and (4) clumps of tracers with no clear kinematical association to close cluster members. Conclusions. We show evidence for a variety of cold substructures predicted in simulations. Most of the streams are kinematically connected to UCDs, supporting the scenario that they can be remnants of disrupted dwarf systems. However, we also show the presence of long coherent substructures connecting cluster members and isolated clumps of tracers possibly left behind by their parent systems before these merged into the central galaxy. Unfortunately, the estimated low-surface brightness of these streams does not allow us to find their signatures in the current imaging data and deeper observations are needed to confirm them

The Fornax Cluster VLT Spectroscopic Survey:IV. cold kinematical substructures in the Fornax core from COSTA

Abstract Context: Substructures in stellar haloes are a strong prediction of galaxy formation models in ΛCDM. Cold streams such as those from small satellite galaxies are extremely difficult to detect and kinematically characterize. The COld STream finder Algorithm (COSTA) is a novel algorithm able to find streams in the phase space of planetary nebulae (PNe) and globular cluster (GC) populations. COSTA isolates groups of (N) particles with small velocity dispersion (between 10 km s−1 and ∼120 km s−1) using an iterative (n) sigma-clipping over a defined number of (k) neighbor particles. Aims: We applied COSTA to a catalog of PNe and GCs from the Fornax Cluster VLT Spectroscopic Survey (FVSS) within ∼200 kpc from the cluster core in order to detect cold substructures and characterize their kinematics (mean velocity and velocity dispersion). Methods: We selected more than 2000 PNe and GCs from the FVSS catalogs and adopted a series of optimized setups of the COSTA parameters based on Montecarlo simulations of the PN and GC populations to search for realistic stream candidates. We find 13 cold substructures with velocity dispersion ranging from ∼20 to ∼100 km s−1, which are likely associated either to large galaxies or to ultra-compact dwarf (UCD) galaxies in the Fornax core. Results: The luminosities of these streams show a clear correlation with internal velocity dispersion, and their surface brightness correlates with their size and distance from the cluster center, which is compatible with the dissipative processes producing them. However, we cannot exclude that some of these substructures formed by violent relaxation of massive satellites that finally merged into the central galaxy. Among these substructures we have: (1) a stream connecting NGC 1387 to the central galaxy, NGC 1399, previously reported in the literature; (2) a new giant stream produced by the interaction of NGC 1382 with NGC 1380 and (possibly) NGC 1381; (3) a series of streams kinematically connected to nearby UCDs; and (4) clumps of tracers with no clear kinematical association to close cluster members. Conclusions: We show evidence for a variety of cold substructures predicted in simulations. Most of the streams are kinematically connected to UCDs, supporting the scenario that they can be remnants of disrupted dwarf systems. However, we also show the presence of long coherent substructures connecting cluster members and isolated clumps of tracers possibly left behind by their parent systems before these merged into the central galaxy. Unfortunately, the estimated low-surface brightness of these streams does not allow us to find their signatures in the current imaging data and deeper observations are needed to confirm them