Formation of ultra-diffuse galaxies in the field and in galaxy groups

Abstract

We study ultra-diffuse galaxies (UDGs) in zoom in cosmological simulations, seeking the origin of UDGs in the field versus galaxy groups. We find that while field UDGs arise from dwarfs in a characteristic mass range by multiple episodes of supernova feedback (Di Cintio et al. 2017), group UDGs may also form by tidal puffing up and they become quiescent by ram-pressure stripping. The field and group UDGs share similar properties, independent of distance from the group centre. Their dark-matter haloes have ordinary spin parameters and centrally dominant dark-matter cores. Their stellar components tend to have a prolate shape with a Sérsic index n ∼ 1 but no significant rotation. Ram pressure removes the gas from the group UDGs when they are at pericentre, quenching star formation in them and making them redder. This generates a colour/star-formation-rate gradient with distance from the centre of the dense environment, as observed in clusters. We find that ∼ 20 per cent of the field UDGs that fall into a massive halo survive as satellite UDGs. In addition, normal field dwarfs on highly eccentric orbits can become UDGs near pericentre due to tidal puffing up, contributing about half of the group-UDG population. We interpret our findings using simple toy models, showing that gas stripping is mostly due to ram pressure rather than tides. We estimate that the energy deposited by tides in the bound component of a satellite over one orbit can cause significant puffing up provided that the orbit is sufficiently eccentric.

Ultra-diffuse galaxies in the Auriga simulations

“…with a median infall redshift of 1.04). The recent simulation work of Jiang et al (2019), which studies satellite UDGs in a group environment, also finds similar formation paths and fractions.…”

“…Note that the UDG sample sizes of the NIHAO and FIRE simulations are quite limited, and comparing to the normal dwarfs in the same mass bin, these simulations may produce over abundant UDGs; see their Fig. 1 and related discussions in Jiang et al (2019).…”

A detailed study of Andromeda XIX, an extreme local analogue of ultradiffuse galaxies

“…Amorisco & Loeb 2016;Rong et al 2017;Chan et al 2018). Further, even when combining feedback with tidal "puffing", the NIHAO simulations (Jiang et al 2019) fail to produce galaxies with sizes and stellar masses comparable to And XIX. Galaxies with half-light radii of ∼ 2 − 3 kpc are typically at least an order of magnitude brighter than And XIX.…”

The origin of low-surface-brightness galaxies in the dwarf regime

“…While these efforts have started to give us a glimpse of the LSBG regime, the galaxy samples that underpin these studies are not representative of the general population of LSBGs. In particular, the statistical properties of LSBGs in groups (e.g Smith Castelli et al 2016;Merritt et al 2016;Román & Trujillo 2017a,b;Jiang et al 2019) and the field (e.g Martínez-Delgado et al 2016a;Papastergis et al 2017;Leisman et al 2017) remain particularly poorly understood, largely due to the lack of surveys that are both deep and wide. However, the successful detection of LSBGs in sparser environments indicates that they are not a cluster phenomenon and are, in fact, a ubiquitous population that inhabits all regions of the observable Universe.…”