Imposters among us: globular cluster kinematics and the halo mass of ultra-diffuse galaxies in clusters

TL;DR

This study uses cosmological simulations to analyze globular cluster kinematics around ultra-diffuse galaxies, confirming GCs as reliable halo mass tracers but highlighting contamination issues affecting observational estimates.

Contribution

It demonstrates that GCs accurately trace UDG halo masses in simulations and emphasizes the impact of intra-cluster GC contamination on observational measurements.

Findings

GCs are good tracers of UDG halo mass in simulations.

Intra-cluster GCs can bias velocity dispersion estimates.

Targets with fewer than 10 GCs have high uncertainties.

Abstract

The velocity dispersion of globular clusters (GCs) around ultra-diffuse galaxies (UDGs) in the Virgo cluster spans a wide range, including cases where GC kinematics suggest halos as massive as (or even more massive than) that of the Milky Way around these faint dwarfs. We analyze the catalogs of GCs derived in post-processing from the TNG50 cosmological simulation to study the GC system kinematics and abundance of simulated UDGs in galaxy groups and clusters. UDGs in this simulation reside exclusively in dwarf-mass halos with $M_{200} \sim 10^{11}$ M$_{\odot}$. When considering only GCs gravitationally bound to simulated UDGs, we find GCs properties that overlap well with several observational measurements for UDGs. In particular, no bias towards overly massive halos is inferred from the study of bound GCs, confirming that GCs are good tracers of UDG halo mass. However, we find that contamination by intra-cluster GCs may, in some cases, substantially increase velocity dispersion estimates when performing projected mock observations of our sample. We caution that targets with less than $10$ GC tracers are particularly prone to severe uncertainties.Measuring the stellar kinematics of the host galaxy should help confirm the unusually massive halos suggested by GC kinematics around some UDGs