From Giants to Dwarfs: A Comprehensive Observational Study of The Globular Cluster System Mass - Halo Mass Relation

Abstract

The scaling relation that exists between the total mass of all globular clusters (GCs) hosted by a galaxy and the total mass of that galaxy, which is dominated by its dark matter halo, has been known and studied for several decades. This GC system (GCS) mass - halo mass relation has been observationally found to apply to nearly every galaxy observed. This relation is remarkably tight, linear, and spans over six orders of magnitude in halo mass. Understanding what drives this linearity and what evolutionary mechanisms affect where a galaxy sits on this relation can allow us to probe both galaxy and GCS evolution. In order to do so, an observational sample of high-quality, homogeneous data, which spans the full range of galaxy masses in the local universe is necessary. This thesis addresses this need through the design of a novel method of determining GC radial density profiles which improves the accuracy and precision of total number of GC estimates for massive galaxies, the application of this method to a sample of 27 brightest cluster galaxies (BCGs), and the compilation of a literature catalog of dwarf galaxy GCSs with standardized GCS and halo mass estimates. With such a complete and methodologically consistent sample we were able to study what properties of GCSs are driving the intrinsic scatter in the relation. We found that, for extremely massive galaxies, positive offset from the relation was associated with more shallow GC radial density profiles, driven specifically by the red GC sub-populations. We also found that ultra diffuse galaxies (UDGs) and extremely low mass and low surface brightness dwarf galaxies were systematically positively offset from the relation compared to their classical dwarf counterparts. BCGs are known to be formed from extensive merger histories, and UDGs are thought to be formed through extreme tidal interactions. Together, these results imply that the merger and tidal histories of galaxies have the greatest affect on the evolution of their GCSs, and by extension, their position on the relation. Studies of GCSs, therefore, are an important tool in tracing galaxy evolution. With this sample, the GCS mass - halo mass relation has been studied comprehensively from the lowest-mass to the highest-mass galaxies in the local universe; the most complete study of its kind to date