The abundance of ultra-diffuse galaxies from groups to clusters: UDGs are relatively more common in more massive haloes

Remco F. J. van der Burg, Henk Hoekstra, Adam Muzzin, Cristobal Sifon, Massimo Viola, Malcolm N. Bremer, Sarah Brough, Simon P. Driver, Thomas Erben, Catherine Heymans, Hendrik Hildebrandt, Benne W. Holwerda, Dominik Klaes, Konrad Kuijken, Sean McGee, Reiko Nakajima, Nicola Napolitano, Peder Norberg, Edward N. Taylor, Edwin Valentijn

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

In recent years, multiple studies have reported substantial populations of large, low-surface-brightness galaxies in local galaxy clusters. Various theories that aim to explain the presence of such ultra-diffuse galaxies (UDGs) have since been proposed. A key question that will help to differentiate between models is whether UDGs have counterparts in lower-mass host haloes, and what their abundance as a function of halo mass is. In this study we extend our previous study of UDGs in galaxy clusters to galaxy groups. We measure the abundance of UDGs in 325 spectroscopically-selected groups from the Galaxy And Mass Assembly (GAMA) survey. We make use of the overlapping imaging from the ESO Kilo-Degree Survey (KiDS), from which we can identify galaxies with mean surface brightnesses within their effective radii down to ~25.5 mag arcsec$^{-2}$ in the r-band. We are able to measure a significant overdensity of UDGs (with sizes r_eff > 1.5 kpc) in galaxy groups down to M200=10^12 Msun, a regime where approximately only 1 in 10 groups contains a UDG that we can detect. We combine measurements of the abundance of UDGs in haloes that cover three orders of magnitude in halo mass, finding that their numbers scale quite steeply with halo mass; N_UDG (R<R200) $\propto$ M200^(1.11+/-0.07). To better interpret this, we also measure the mass-richness relation for brighter galaxies down to $M^*_r$+2.5 in the same GAMA groups, and find a much shallower relation of N_Bright (R<R200) $\propto$ M200^(0.78+/-0.05). This shows that UDGs are relatively more abundant, compared to bright galaxies, in massive clusters than in groups. We discuss implications, but whether this difference is related to a higher destruction rate of UDGs in groups, or whether massive haloes have a positive effect on their formation, is not yet clear.
Original languageEnglish
Article numberA79
Number of pages13
JournalAstronomy and Astrophysics
Volume607
Early online date17 Nov 2017
DOIs
Publication statusPublished - Nov 2017

Keywords

  • Galaxies: dwarf
  • Galaxies: formation
  • Galaxies: evolution
  • Galaxies: structure
  • Galaxies: groups: general
  • Galaxies: clusters: general

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