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6C1D7581-7C74-4478-B287-6A89DF370CD1

# Origin and evolution of ultra-diffuse galaxies in different environments

Jose A. Benavides, Laura V. Sales, Mario. G. Abadi, Federico Marinacci, Mark Vogelsberger, Lars Hernquist

Submitted on 15 September 2022

## Abstract

We study the formation of ultra-diffuse galaxies (UDGs) using the cosmological hydrodynamical simulation TNG50 of the Illustris-TNG suite. We define UDGs as dwarf galaxies in the stellar mass range $7.5\le \mathrm{l}\mathrm{o}\mathrm{g}\left({\mathrm{M}}_{\star }/{\mathrm{M}}_{\odot }\right)\le 9$ that are in the $5\mathrm{%}$ most extended tail of the simulated mass-size relation. This results in a sample of UDGs with half-mass radii and surface brightness between $24.5$ and , similar to definitions of UDGs in observations. The large cosmological volume in TNG50 allows for a comparison of UDGs properties in different environments, from the field to galaxy clusters with virial mass . All UDGs in our sample have dwarf-mass haloes () and show the same environmental trends as normal dwarfs: field UDGs are star-forming and blue while satellite UDGs are typically quiescent and red. The TNG50 simulation predicts UDGs that populate preferentially higher spin haloes and more massive haloes at fixed ${\mathrm{M}}_{\star }$ compared to non-UDG dwarfs. This applies also to most satellite UDGs, which are actually born" UDGs in the field and infall into groups and clusters without significant changes to their size. We find, however, a small subset of satellite UDGs ($\lesssim 10\mathrm{%}$) with present-day stellar size a factor $\ge 1.5$ larger than at infall, confirming that tidal effects, particularly in the lower mass dwarfs, are also a viable formation mechanism for some of these dwarfs, although subdominant in this simulation.

## Preprint

Comment: 17 pages, 13 figures, submitted to MNRAS

Subject: Astrophysics - Astrophysics of Galaxies