A high occurrence of nuclear star clusters in faint Coma galaxies, and the roles of mass and environment

Abstract

We use deep high resolution HST/ACS imaging of two fields in the core of the Coma cluster to investigate the occurrence of nuclear star clusters (NSCs) in quiescent dwarf galaxies as faint as M I = −10 mag. We employ a hierarchical Bayesian logistic regression framework to model the faint end of the nucleation fraction ( f n ) as a function of both galaxy luminosity and environment. We find that f n is remarkably high in Coma: at M I ≈ −13 mag half of the cluster dwarfs still host prominent NSCs. Comparison with dwarf systems in nearby clusters and groups shows that, within the uncertainties, the rate at which the probability of nucleation varies with galaxy luminosity is nearly universal. On the other hand, the fraction of nucleated galaxies at fixed luminosity does exhibit an environmental dependence. More massive environments feature higher nucleation fractions and fainter values of the half-nucleation luminosity, which roughly scales with host halo virial mass as L I, f n50 ∝ M −0.2 200 . Our results reinforce the role of galaxy mass as a major driver of the efficiency of NSC formation and also indicate a clear secondary dependence on the environment, hence paving the way to more refined theoretical models.

ELVES II: Globular Clusters and Nuclear Star Clusters of Dwarf Galaxies: the Importance of Environment

“…Very recently, Zanatta et al (2021) also confirmed this environmental trend comparing satellites in different mass clusters and lower mass, LV hosts. For the latter, they used satellites partly from the surveys of Carlsten et al (2020a,b).…”

“…While the inner LV nucleation fractions are still slightly below that of the Virgo sample, the difference is much less. This brings up the intriguing possibility that the difference seen in the left panel and reported by Sánchez-Janssen et al (2019) and Zanatta et al (2021) is actually more of an effect of the cluster samples being very centralized and less due to the parent halo mass in which the dwarfs reside. Unfortunately we do not have the dwarf samples to conclusively show which affect (parent halo mass or location of dwarf within parent halo) is dominant.…”

“…We have greatly increased the statistics for LV satellites since those works. Additionally, Zanatta et al (2021) include all confirmed and 'possible' satellites (candidate satellites where the SBF distances were inconclusive) from those works. From our experience with acquiring deeper follow-up, we suspect roughly half of the latter class are background objects.…”

“…The spatial distribution of nucleated dE's in Fornax and Virgo are more centrally concentrated than non-nucleated dE's (Lisker et al 2007;Ordenes-Briceño et al 2018b). Additionally, dEs in higher mass clusters, like Coma, are nucleated at a higher frequency than in Virgo or Fornax (den Brok et al 2014;Sánchez-Janssen et al 2019;Zanatta et al 2021). Sánchez-Janssen et al (2019) tentatively showed that the nucleation fraction is even lower in the Local Group (LG); however, the statistics afforded by just the LG are not enough to make a strong conclusion.…”

Structure and morphology of the MATLAS dwarf galaxies and their central nuclei

“…This migration can then be followed by a merger with another cluster. Dwarf galaxies are also known to host active galactic nuclei (AGN; e.g, Marleau et al 2013Marleau et al , 2017Kaviraj et al 2019;Mezcua & Domínguez Sánchez 2020;Molina et al 2021) or both NSC and AGN (Côté et al 2006;den Brok et al 2015).…”