Extending the Globular Cluster System-Halo Mass Relation to the Lowest Galaxy Masses

TL;DR

This study extends the globular cluster system-halo mass relation down to low-mass dwarf galaxies, revealing increased scatter and challenging existing models, with implications for understanding GC formation in small halos.

Contribution

The paper provides the first empirical extension of the GC system-halo mass relation to dwarf galaxies below 10^9 M_sun, using new halo mass estimates from stellar and gas kinematics.

Findings

GC system-halo mass relation holds down to 10^9 M_sun halos.

Significant scatter and wide GC-to-halo mass ratios in ultra diffuse galaxies.

Discrepancy with existing models suggests more efficient GC formation or stochastic occupation in low-mass halos.

Abstract

High mass galaxies, with halo masses $M_{200} \ge 10^{10} M_{\odot}$, reveal a remarkable near-linear relation between their globular cluster (GC) system mass and their host galaxy halo mass. Extending this relation to the mass range of dwarf galaxies has been problematic due to the difficulty in measuring independent halo masses. Here we derive new halo masses based on stellar and HI gas kinematics for a sample of nearby dwarf galaxies with GC systems. We find that the GC system mass--halo mass relation for galaxies populated by GCs holds from halo masses of $M_{200} \sim 10^{14} M_{\odot}$ down to below $M_{200}$ $\sim 10^9 M_{\odot}$, although there is a substantial increase in scatter towards low masses. In particular, three well-studied ultra diffuse galaxies, with dwarf-like stellar masses, reveal a wide range in their GC-to-halo mass ratios. We compare our GC system--halo mass relation to the recent model of El Badry et al., finding that their fiducial model does not reproduce our data in the low mass regime. This may suggest that GC formation needs to be more efficient than assumed in their model, or it may be due to the onset of stochastic GC occupation in low mass halos. Finally, we briefly discuss the stellar mass-halo mass relation for our low mass galaxies with GCs, and we suggest some nearby dwarf galaxies for which searches for GCs may be fruitful.