# Ultra-diffuse galaxies in the Auriga simulations

## TL;DR

This study uses the Auriga simulations to explore how ultra-diffuse galaxies form, revealing their properties, origins, and the role of dark matter halo spin and tidal interactions.

## Contribution

It provides the first detailed analysis of UDG formation in cosmological simulations, linking galaxy properties to dark matter halo characteristics and environmental effects.

## Key findings

- UDGs in simulations match observed properties.
- Field UDGs form in high-spin dark matter haloes.
- Satellite UDGs originate from pre-existing UDGs or tidal interactions.

## Abstract

We investigate the formation of ultra-diffuse galaxies (UDGs) using the Auriga high-resolution cosmological magneto-hydrodynamical simulations of Milky Way-sized galaxies. We identify a sample of $92$ UDGs in the simulations that match a wide range of observables such as sizes, central surface brightness, S\'{e}rsic indices, colors, spatial distribution and abundance. Auriga UDGs have dynamical masses similar to normal dwarfs. In the field, the key to their origin is a strong correlation present in low-mass dark matter haloes between galaxy size and halo spin parameter. Field UDGs form in dark matter haloes with larger spins compared to normal dwarfs in the field, in agreement with previous semi-analytical models. Satellite UDGs, on the other hand, have two different origins: $\sim 55\%$ of them formed as field UDGs before they were accreted; the remaining $\sim 45\%$ were normal field dwarfs that subsequently turned into UDGs as a result of tidal interactions.