Origin and evolution of ultradiffuse galaxies in different environments

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 $\rm {7.5 \le log (M_{\star } / M_{\odot }) \le 9 }$ that are in the $5\%$ most extended tail of the simulated mass-size relation. This results in a sample of UDGs with half-mass radii $\rm {r_{h \star } \gtrsim 2 \ kpc}$ and surface brightness between $\rm {24.5}$ and $\rm {28 \ mag \ arcsec^{-2}}$, 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 $\rm {M_{200} \sim 2 \times 10^{14} ~ M_{\odot }}$. All UDGs in our sample have dwarf-mass haloes ($\rm {M_{200}\sim 10^{11} ~ M_{\odot } }$) 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 $\rm {M_{\star }}$ 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 ($\lesssim 10 \%$) with present-day stellar size a factor ≥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.

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

“…Note that secondary halo properties are also nontrivially correlated with the resulting UDG properties in CDM (e.g.,Benavides et al 2021Benavides et al , 2023.…”

The Next Generation Virgo Cluster Survey (NGVS). XXXV. First Kinematical Clues of Overly Massive Dark Matter Halos in Several Ultradiffuse Galaxies in the Virgo Cluster

“…Using 14 Virgo-like clusters from the Illustris TNG100 cosmological hydrodynamical simulation, Sales et al (2020) found two main paths to form cluster UDGs: (a) born UDGs are field low surface brightness galaxies that recently (∼6 Gyr ago median, albeit with significant dispersion) entered the cluster and now show large amounts of dark matter and have stellar populations with intermediate ages and low metallicities, and (b) tidal UDGs are higher surface brightness galaxies that fell into the cluster early on and, as a consequence, have little to no dark matter left, old stellar ages, and high metallicities. Note that born UDGs could correspond to several internal mechanisms discussed in the literature, such as strong feedback (Di Cintio et al 2017;Chan et al 2018) or high-spin halos (Amorisco & Loeb 2016;Benavides et al 2023).…”

“…For instance, in current state-of-the-art cosmological numerical simulations such as TNG50, which models a cosmological volume large enough to include some spread in environment and accretion histories, UDGs are formed via high-spin halos and, to lesser degree, dynamical heating, with the expectation that they all inhabit dwarf-mass dark matter halos (Benavides et al 2023). All other cosmological simulations that include high-density environments find a combination of processes involving feedback and environment, but in not a single case is a failed galaxy compatible with our measurement predicted (Di Cintio et al 2017;Chan et al 2018;Jiang et al 2019;Tremmel et al 2020).…”

“…Such results favoring dwarf-mass halos for UDGs are a confirmation that these galaxies have normal efficiencies at turning baryons into stars; they just do it in a very extended configuration. Several theoretical models have indeed been proposed to explain the large radii of UDGs in dwarf-mass halos, which include internal mechanisms such as halos with large spins (Amorisco & Loeb 2016;Rong et al 2017;Benavides et al 2023) or low concentrations (Kong et al 2022) or dwarfs expanded as the result of repetitive and disruptive feedback events (Di Cintio et al 2017;Chan et al 2018) or early mergers (Wright et al 2021), as well as external, environmentally driven processes, such as tidal heating and stripping (Safarzadeh & Scannapieco 2017;Carleton et al 2019), quenching and dimming (Tremmel et al 2020), or a combination of internal and external mechanisms (Jiang et al 2019;Sales et al 2020). From the numerical simulations standpoint, it seems like the existence of a population of UDGs living in dwarf-mass halos is not challenging but rather a natural prediction of ΛCDM.…”

Beyond Ultra-diffuse Galaxies. I. Mass–Size Outliers among the Satellites of Milky Way Analogs

“…Various mechanisms have been proposed to explain the presence of large, diffuse galaxies (as mass-size outliers) across different environments. In the field (i.e., in isolation), their large sizes might be a result of stellar feedback (Di Cintio et al 2017;Chan et al 2018), early galaxy mergers (Wright et al 2021), passing into and out of a more massive halo (socalled backsplash satellites; Benavides et al 2021), or of inhabiting halos with higher spins (Dalcanton et al 1997;Amorisco & Loeb 2016;Liao et al 2019;Mancera Piña et al 2020;Benavides et al 2023; Kong et al 2022). In groups and Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.…”