An excess of globular clusters in Ultra-Diffuse Galaxies formed through tidal heating

Abstract

To investigate the origin of elevated globular cluster (GC) abundances observed around Ultra-Diffuse Galaxies (UDGs), we simulate GC populations hosted by UDGs formed through tidal heating. Specifically, GC formation is modelled as occurring in regions of dense star formation. Because star formation-rate densities are higher at high redshift, dwarf galaxies in massive galaxy clusters, which formed most of their stars at high redshift, form a large fraction of their stars in GCs. Given that UDGs formed through environmental processes are more likely to be accreted at high redshift, these systems have more GCs than non-UDGs. In particular, our model predicts that massive UDGs have twice the GC mass of non-UDGs of similar stellar mass, in rough agreement with observations. Although this effect is somewhat diminished by GC disruption, we find that the relationship between GC mass fraction and cluster-centric distance, and the relationship between GC mass fraction and galaxy half-light radius are remarkably similar to observations. Among our model objects, both UDGs and non-UDGs present a correlation between halo mass and GC mass, although UDGs have lower dynamical masses at a given GC mass. Furthermore, because of the effectiveness of GC disruption, we predict that GCs around UDGs should have a more top heavy mass function than GCs around non-UDGs. This analysis suggests that dwarfs with older stellar populations, such as UDGs, should have higher GC mass fractions than objects with young stellar populations, such as isolated dwarfs.

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

“…17 includes galaxies in the Virgo cluster (Peng et al 2008;Carlsten et al 2021), the Fornax cluster (ACSFCS, Liu et al 2019) and galaxy groups in the local volume (Carlsten et al 2021). Our UDGs are in the Coma cluster, which is more massive than the other two clusters, and the relative increase in 𝑁 GC at a given stellar mass may be an indication of environmental effects in GC formation or UDG evolution (Peng et al 2008;Carleton et al 2021;Carlsten et al 2021). It is noteworthy that among the best-studied UDGs in term of their GCs, the UDG known as MATLAS-2019 (Habas et al 2020) with 𝑅 e = 2.2 kpc (smaller effective radius than our UDGs) shows a large number of GCs for its stellar mass (Müller et al 2021;Danieli et al 2021).…”

“…Nonetheless, they are well within the global distribution considering the scatter of the relation. As noted by Carleton et al (2021), whose model attributes such an offset not to an overabundance of GCs but rather to a paucity of stars in UDGs, there are different ways to view the result. Because we do not have independent measurements of 𝑀 total for the full sample, we cannot yet determine if these systems Figure 17.…”

“…Even without this additional complication, it is evident from this discussion that theoretical expectations for the number and properties of GCs in the various UDG formation/evolution models need further development. Fortunately, some studies have begun this exploration in detail for specific models (Carleton et al 2021). Our goal here is to motivate further work by providing higher fidelity GC observations against which to do the comparison.…”

Ultra-Diffuse Galaxies in the Perseus Cluster: Comparing Galaxy Properties with Globular Cluster System Richness

“…Early infall times will quench star formation resulting in a passively evolving stellar population that will slowly decrease in surface brightness (e.g, Yozin & Bekki 2015;Román & Trujillo 2017;Chan et al 2018;Jiang et al 2019;Sales et al 2020;Tremmel et al 2020). Additionally, UDGs that fall in earlier will spend more time being subject to the cluster's tidal forces, which can play an important role in heating and expanding UDG stellar populations, giving rise to their large sizes (Yozin & Bekki 2015;Jiang et al 2019;Martin et al 2019;Sales et al 2020;Carleton et al 2019Carleton et al , 2021. Other mechanisms (e.g., high halo spin; Amorisco & Loeb 2016;Rong et al 2017;Mancera Piña et al 2020) and combinations of mechanisms (e.g., stellar feedback and quenching, Chan et al 2018 or stellar feedback and tides, Jiang et al 2019) have also been considered.…”

“…Large cosmological simulations of galaxy formation do not (yet) have the resolution to properly resolve GC formation. Probing galaxy GC formation requires either the implementation of specialised simulations for single galaxies (e.g., Dutta Chowdhury et al 2020) or additional sub-grid/semi-analytic modelling within the simulation (e.g., Carleton et al 2021;Doppel et al 2021). To date, only one work has applied such semi-analytic models to a cosmological simulation to investigate GC formation in UDGs.…”