# The Formation of Ultra-Diffuse Galaxies in the RomulusC Galaxy Cluster Simulation

## TL;DR

This study uses the RomulusC simulation to explore the origins of ultra-diffuse galaxies in clusters, revealing they are mainly quenched dwarf galaxies affected by early infall, tidal interactions, and stellar evolution.

## Contribution

It demonstrates that UDGs form from typical dwarf galaxies in clusters through environmental effects, with detailed insights into their evolution and properties.

## Key findings

- UDGs are similar to other dwarfs but are quenched.
- Tidal interactions cause dark matter stripping and stellar expansion.
- UDGs originate from early-infall dwarf galaxies undergoing passive evolution.

## Abstract

We study the origins of 122 ultra-diffuse galaxies (UDGs) in the {\sc RomulusC} zoom-in cosmological simulation of a galaxy cluster (M$_{200} = 1.15\times10^{14}$ M$_{\odot}$), one of the only such simulations capable of resolving the evolution and structure of dwarf galaxies (M$_{\star} < 10^9$ M$_{\odot}$). We find broad agreement with observed cluster UDGs and predict that they are not separate from the overall cluster dwarf population. UDGs in cluster environments form primarily from dwarf galaxies that experienced early cluster in-fall and subsequent quenching due to ram pressure. The ensuing dimming of these dwarf galaxies due to passive stellar evolution results in a population of very low surface brightness galaxies that are otherwise typical dwarfs. UDGs and non-UDGs alike are affected by tidal interactions with the cluster potential. Tidal stripping of dark matter, as well as mass loss from stellar evolution, results in the adiabatic expansion of stars, particularly in the lowest mass dwarfs. High mass dwarf galaxies show signatures of tidal heating while low mass dwarfs that survive until $z=0$ typically have not experienced such impulsive interactions. There is little difference between UDGs and non-UDGs in terms of their dark matter halos, stellar morphology, colors, and location within the cluster. In most respects cluster UDG and non-UDGs alike are similar to isolated dwarf galaxies, except for the fact that they are typically quenched.