The Distribution of Ultra-diffuse and Ultra-compact Galaxies in the Frontier Fields

Abstract

Large low surface brightness galaxies have recently been found to be abundant in nearby galaxy clusters. In this paper, we investigate these ultra-diffuse galaxies (UDGs) in the six Hubble Frontier Fields galaxy clusters: Abell 2744, MACSJ0416.1−2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063 and Abell 370. These are the most massive (1-3 × 10 15 M ) and distant (0.308 < z < 0.545) systems in which this class of galaxy has yet been discovered. We estimate that the clusters host of the order of ∼200-1400 UDGs inside the virial radius (R 200 ), consistent with the UDG abundance halo-mass relation found in the local universe, and suggests that UDGs may be formed in clusters. Within each cluster, however, we find that UDGs are not evenly distributed. Instead their projected spatial distributions are lopsided, and they are deficient in the regions of highest mass density as traced by gravitational lensing. While the deficiency of UDGs in central regions is not surprising, the lopsidedness is puzzling. The UDGs, and their lopsided spatial distributions, may be associated with known substructures late in their infall into the clusters, meaning that we find evidence both for formation of UDGs in clusters and for UDGs falling into clusters. We also investigate the ultracompact dwarfs (UCDs) residing in the clusters, and find the spatial distributions of UDGs and UCDs appear anti-correlated. Around 15% of UDGs exhibit either compact nuclei or nearby point sources. Taken together, these observations provide additional evidence for a picture in which at least some UDGs are destroyed in dense cluster environments and leave behind a residue of UCDs.

Keck Cosmic Web Imager (KCWI) spectra of globular clusters and ultracompact dwarfs in the halo of M87

“…Alabi et al 2020, submitted). This can be contrasted with the rise in space density of UCDs towards the centre of those clusters, suggesting one type of galaxy is transformed into another (Janssens et al 2017;Janssens et al 2019). Alpha-element abundances are not generally available for Virgo cluster ultra diffuse galaxies but they do exist for Coma cluster ones (see Ferré-Mateu et al 2018 and references therein).…”

The first detection of ultra-diffuse galaxies in the Hydra I cluster from the VEGAS survey

“…Taking into account the virial mass of the Hydra I cluster (2 × 10 14 M , Girardi et al 1998), from the abundance-halo mass relation (Janssens et al 2019) we expect up to 100 UDGs inside the cluster virial radius. A follow-up study, in which the UDG detection is not carried out visually, but using automated tools already tested on the Fornax galaxy cluster (Venhola et al 2019), is in progress.…”

“…Leisman et al 2017;Román & Trujillo 2017;Prole et al 2019b). The spatial distribution of UDGs inside their host environment seems to be asymmetric, meaning overdensities of UDGs are found close to sub-structures, as subgroups of galaxies, which are falling into the cluster (van der Burg et al 2017;Janssens et al 2019).…”

Formation of an ultra-diffuse galaxy in the stellar filaments of NGC 3314A: Caught in the act?

“…To date, a significant population of UDGs has been found in dense environments, such as clusters and groups of galaxies, as well as in the field (Koda et al 2015;Román & Trujillo 2017;van der Burg et al 2017;Shi et al 2017;Müller et al 2018;Venhola et al 2017;Prole et al 2019b;Forbes et al 2019;Janssens et al 2019;Forbes et al 2020b;Habas et al 2020). Based on their colour distribution, morphology, stellar popula-tion, and globular cluster (GC) systems, a wide range of observed properties are found for UDGs, which do not fit into a single formation scenario (Leisman et al 2017;Román & Trujillo 2017;Ferré-Mateu et al 2018;Martín-Navarro et al 2019;Lim et al 2020;Forbes et al 2020a;Rong et al 2020).…”