The impact of galaxy harassment on the globular cluster systems of early-type cluster dwarf galaxies

TL;DR

This study uses numerical simulations to examine how galaxy harassment affects globular cluster systems in early-type dwarf galaxies within clusters, revealing the conditions under which GCS dynamics reliably indicate galaxy mass.

Contribution

It introduces a detailed analysis of the impact of tidal harassment on GCSs, highlighting the role of dark matter fraction in the reliability of mass estimates from GCS dynamics.

Findings

GCS dynamics remain reliable for mass estimation when dark matter fraction is above ~15%.

Unbound GCs quickly separate, reducing their impact on observed velocity dispersion.

Complete disruption occurs when dark matter fraction drops below 3%, invalidating GCS-based mass estimates.

Abstract

The dynamics of globular cluster systems (GCSs) around galaxies are often used to assess the total enclosed mass, and even to constrain the dark matter distribution. The globular cluster system of a galaxy is typically assumed to be in dynamical equilibrium within the potential of the host galaxy. However cluster galaxies are subjected to a rapidly evolving and, at times, violently destructive tidal field. We investigate the impact of the harassment on the dynamics of GCs surrounding early type cluster dwarfs, using numerical simulations. We find that the dynamical behaviour of the GCS is strongly influenced by the fraction of bound dark matter f_{DM} remaining in the galaxy. Only when f_{DM} falls to ~15%, do stars and GCs begin to be stripped. Still the observed GC velocity dispersion can be used to measure the true enclosed mass to within a factor of 2, even when f_{DM} falls as low as ~3%. This is possible partly because unbound GCs quickly separate from the galaxy body. However even the distribution of {\it{bound}} GCs may spatially expand by a factor of 2-3. Once f_{DM} falls into the <3% regime, the galaxy is close to complete disruption, and GCS dynamics can no longer be used to reliably estimate the enclosed mass. In this regime, the remaining bound GCS may spatially expand by a factor of 4 to 8. It may be possible to test if a galaxy is in this regime by measuring the dynamics of the stellar disk. We demonstrate that if a stellar disk is rotationally supported, it is likely that a galaxy has sufficient dark matter, that the dynamics of the GCS can be used to reliably estimate the enclosed mass.