The formation of ultradiffuse galaxies in the RomulusC galaxy cluster simulation

Abstract

We study the origins of 122 ultra-diffuse galaxies (UDGs) in the RomulusC zoom-in cosmological simulation of a galaxy cluster (M200 = 1.15 × 1014 M⊙), one of the only such simulations capable of resolving the evolution and structure of dwarf galaxies (M⋆ < 109 M⊙). 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.

Transforming gas-rich low-mass disky galaxies into ultra-diffuse galaxies by ram pressure

“…10 Gyr) can be neglected when a galaxy has a massive dark matter halo. However, numerical simulations 33 suggest that a dark matter halo will be gradually stripped by tidal interactions with other galaxy cluster members during flybys, which would cause the overall stellar disc expansion by about 25% over 10 Gyr. Assuming passive evolution, based on best-fitting stellar population parameters and a slow disc expansion, we can predict internal properties (luminosity, surface brightness, luminosity-and mass-weighted stellar metallicities) of our galaxies up-to 10 Gyr from now (Figure 4).…”

Shadows in the Dark: Low-surface-brightness Galaxies Discovered in the Dark Energy Survey

“…As extremes in the relationship between galaxy size and luminosity, LSBGs provide a litmus test for models that predict galaxy properties from cosmological principles (e.g., Ferrero et al 2012;Papastergis et al 2015). It has been suggested that LSBGs form naturally within the ΛCDM framework, either primordially in halos with high angular velocity (Dalcanton et al 1997;Amorisco & Loeb 2016) or through evolution in dense environments (Tremmel et al 2020;Martin et al 2019). On the other hand, observations of LSBGs with anomalously low dark matter content (van Dokkum et al 2018(van Dokkum et al , 2019 may necessitate modified models of galaxy formation (e.g., Papastergis et al 2017;Sales et al 2020) and/ or dark matter physics (e.g., Carleton et al 2019).…”

Implications for Galaxy Formation Models from Observations of Globular Clusters around Ultra-Diffuse Galaxies

“…• The initial UDG studies suggested that UDGs represent a population of failed galaxies that assembled their dark matter haloes and were rapidly quenched at high redshift due to environmental processes in galaxy clusters, mainly ram pressure stripping (van Dokkum et al 2015a;Koda et al 2015;Yozin & Bekki 2015;Benavides et al 2021). Additionally, as a consequence of the passive evolution of their stellar populations, UDGs surface brightness have decreased with time (Román & Trujillo 2017;Román et al 2019;Tremmel et al 2020). This scenario is consistent with observations of cluster UDGs as gas-poor (Karunakaran et al 2020;Chen et al 2020) quiescent (Singh et al 2019), old, metal-poor, and alpha-enhanced (Kadowaki et al 2017;Gu et al 2018;Pandya et al 2018;Ruiz-Lara et al 2018;Ferré-Mateu et al 2018).…”