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Register a new userThe evolution of ultra-diffuse galaxies in nearby galaxy clusters from the Kapteyn IAC WEAVE INT Clusters Survey ($texttt{KIWICS}$)
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Added by
Pavel Mancera Pi\\~na
Publication date
2019
fields
Physics
and research's language is
English
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We study the population of ultra-diffuse galaxies (UDGs) in a set of eight nearby ($z <$ 0.035) galaxy clusters, from the Kapteyn IAC WEAVE INT Clusters Survey ($texttt{KIWICS}$). We report the discovery of 442 UDG candidates in our eight field of views, with 247 of these galaxies lying at projected distances < 1 R$_{200}$ from their host cluster. With the aim of testing theories about their formation, we study the scaling relations of UDGs comparing with different types of galaxies, finding that in the full parameter space they behave as dwarf galaxies and their colors do not seem to correlate with their effective radii. To investigate the influence of the environment on the evolution of UDGs we analyze their structural properties as functions of the projected clustercentric distance and the mass of their host cluster. We find no systematic trends for the stellar mass nor effective radius as function of the projected distance. However, the fraction of blue UDGs seems to be lower towards the center of clusters, and UDGs in the inner and outer regions of clusters have different Sersic index and axis ratio distributions. Specifically, the axis ratio distributions of the outer and inner UDGs resemble the axis ratio distributions of, respectively, late-type dwarfs and dwarf ellipticals in the Fornax Cluster suggesting an environmentally-driven evolution and another link between UDGs and dwarf galaxies. In general our results suggest strong similarities between UDGs and smaller dwarf galaxies in their structural parameters and their transformation within clusters.
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The number of Ultra-Diffuse Galaxies (UDGs) in clusters is of significant importance to constrain models of their formation and evolution. Furthermore, their distribution inside clusters may tell us something about their interactions with their environments. In this work we revisit the abundance of UDGs in a more consistent way than in previous studies. We add new data of UDGs in eight clusters from the Kapteyn IAC WEAVE INT Clusters Survey (KIWICS), covering a mass range in which only a few clusters have been studied before, and complement these with a compilation of works in the literature to homogeneously study the relation between the number of UDGs and the mass of their host cluster. Overall, we find that the slope of the number of UDGs$-$cluster mass relation is consistent with being sublinear when considering galaxy groups or linear if they are excluded, but we argue that most likely the behavior is sublinear. When systematically studying the relation between the projected distance to the innermost UDG and M$_{200}$ for each cluster, we find hints that favor a picture in which massive clusters destroy UDGs in their centres.
We analyse a sample of twelve galaxy clusters, from the Kapteyn IAC WEAVE INT Cluster Survey (KIWICS) looking for dwarf galaxy candidates. By using photometric data in the $r$ and $g$ bands from the Wide Field Camera (WFC) at the 2.5-m Isaac Newton telescope (INT), we select a sample of bright dwarf galaxies (M$_r$ $leq$ -15.5 mag) in each cluster and analyse their spatial distribution, stellar colour, and as well as their Sersic index and effective radius. We quantify the dwarf fraction inside the $R_{200}$ radius of each cluster, which ranges from $sim$ 0.7 to $sim$ 0.9. Additionally, when comparing the fraction in the inner region with the outermost region of the clusters, we find that the fraction of dwarfs tends to increase going to the outer regions. We also study the clustercentric distance distribution of dwarf and giant galaxies (M$_r$ $<$ -19.0 mag), and in half of the clusters of our sample, the dwarfs are distributed in a statistically different way as the giants, with the giant galaxies being closer to the cluster centre. We analyse the stellar colour of the dwarf candidates and quantify the fraction of blue dwarfs inside the $R_{200}$ radius, which is found to be less than $sim$ 0.4, but increases with distance from the cluster centre. Regarding the structural parameters, the Sersic index for the dwarfs we visually classify as early type dwarfs tends to be higher in the inner region of the cluster. These results indicate the role that the cluster environment plays in shaping the observational properties of low-mass halos.
We use the IllustrisTNG cosmological hydrodynamical simulation to study the formation of ultra-diffuse galaxies (UDGs) in galaxy clusters. We supplement the simulations with a realistic mass-size relation for galaxies at the time of infall into the cluster, as well as an analytical model to describe the tidally-induced evolution of their stellar mass, velocity dispersion and size. The model assumes cuspy NFW halos and, contrary to recent claims, has no difficulty reproducing the observed number of UDGs in clusters. Our results further suggest that the UDG population consists of a mixture of normal low surface brightness galaxies such as those found in the field (born UDGs, or B-UDGs), as well as a distinct population that owe their large size and low surface brightness to the effects of cluster tides (tidal, or T-UDGs). The simulations indicate that T-UDGs entered the cluster earlier and should be more prevalent than B-UDGs near the cluster centres. T-UDGs should also have, at given stellar mass, lower velocity dispersion, higher metallicities, and lower dark matter content than B-UDGs. Our results suggest that systems like DF-44 are consistent with having been born as UDGs, while others such as DF2, DF4 and VLSB-D are possibly extreme T-UDG examples.
We present an analysis of archival {it HST/ACS} imaging in the F475W ($g_{475}$), F606W ($V_{606}$) and F814W ($I_{814}$) bands of the globular cluster (GC) system of a large (3.4 kpc effective radius) ultra-diffuse galaxy (DF17) believed located in the Coma Cluster of galaxies. We detect 11 GCs down to the 5$sigma$ completeness limit of the imaging ($I_{814}=$27 mag). Correcting for background and our detection limits yields a total population of GCs in this galaxy of $27pm5$ and a $V$-band specific frequency, $S_N=28pm5$. Based on comparisons to the GC systems of Local galaxies, we show that both the absolute number and the colors of the GC system of DF17 are consistent with the GC system of a dark-matter dominated dwarf galaxy with virial mass $sim0.9times10^{10}$~msun and a dark-to-stellar mass ratio, $M_{vir} / M_{ star}sim 1000$. Based on the stellar mass-growth of the Milky Way, we show that DF17 cannot be understood as a failed Milky Way-like system, but is more similar to quenched Large Magellanic Cloud-like systems. We find that the mean color of GC population, $g_{475}-I_{814}$ = $0.91pm0.05$ mag, coincides with the peak of the color distribution of intracluster GCs and are also similar to those of the blue GCs in the outer regions of massive galaxies. We suggest that both the intracluster GC population in Coma and the blue-peak in the GC populations of massive galaxies may be fed - at least in part - by the disrupted equivalents of systems such as DF17.
Ultra-compact dwarf galaxies (UCDs) are predominatly found in the cores of nearby galaxy clusters. Besides the Fornax and Virgo cluster, UCDs have also been confirmed in the twice as distant Hydra I and Centaurus clusters. Having (nearly) complete samples of UCDs in some of these clusters allows the study of the bulk properties with respect to the environment they are living in. Moreover, the relation of UCDs to other stellar systems in galaxy clusters, like globular clusters and dwarf ellipticals, can be investigated in detail with the present data sets. The general finding is that UCDs seem to be a heterogenous class of objects. Their spatial distribution within the clusters is in between those of globular clusters and dwarf ellipticals. In the colour-magnitude diagram, blue/metal-poor UCDs coincide with the sequence of nuclear star clusters, whereas red/metal-rich UCDs reach to higher masses and might have originated from the amalgamation of massive star cluster complexes in merger or starburst galaxies.
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