The physics governing the upper truncation mass of the globular cluster mass function

Abstract

ABSTRACT The mass function of globular cluster (GC) populations is a fundamental observable that encodes the physical conditions under which these massive stellar clusters formed and evolved. The high-mass end of star cluster mass functions are commonly described using a Schechter function, with an exponential truncation mass Mc, *. For the GC mass functions in the Virgo galaxy cluster, this truncation mass increases with galaxy mass (M*). In this paper, we fit Schechter mass functions to the GCs in the most massive galaxy group ($M_{\mathrm{200}} = 5.14 \times 10^{13} \, {\rm M}_{\odot }$) in the E-MOSAICS simulations. The fiducial cluster formation model in E-MOSAICS reproduces the observed trend of Mc, * with M* for the Virgo cluster. We therefore examine the origin of the relation by fitting Mc, * as a function of galaxy mass, with and without accounting for mass loss by two-body relaxation, tidal shocks and/or dynamical friction. In the absence of these mass-loss mechanisms, the Mc, *-M* relation is flat above $M_* \gt 10^{10}\, {\rm M}_{\odot }$. It is therefore the disruption of high-mass GCs in galaxies with $M_{*}\sim 10^{10} \, {\rm M}_{\odot }$ that lowers the Mc, * in these galaxies. High-mass GCs are able to survive in more massive galaxies, since there are more mergers to facilitate their redistribution to less-dense environments. The Mc, * − M* relation is therefore a consequence of both the formation conditions of massive star clusters and their environmentally dependent disruption mechanisms.