The SLUGGS Survey: globular clusters and the dark matter content of early-type galaxies

TL;DR

This study reveals a strong correlation between blue globular clusters and dark matter content in early-type galaxies, enabling dark matter estimates from GC imaging and providing insights into galaxy formation and evolution.

Contribution

It demonstrates a direct, galaxy-scale link between blue globular clusters and dark matter, refining methods to estimate dark matter content from GC system observations.

Findings

Blue GC systems correlate strongly with dark matter mass.

Dark matter mass can be estimated within a factor of two from GC imaging.

Galaxies with more blue GCs tend to have higher dark matter fractions.

Abstract

A strong correlation exists between the total mass of a globular cluster (GC) system and the virial halo mass of the host galaxy. However, the total halo mass in this correlation is a statistical measure conducted on spatial scales that are some ten times that of a typical GC system. Here we investigate the connection between GC systems and galaxy's dark matter on comparable spatial scales, using dynamical masses measured on a galaxy-by-galaxy basis. Our sample consists of 17 well-studied massive (stellar mass $\sim$10$^{11}$ M$_{\odot}$) early-type galaxies from the SLUGGS survey. We find the strongest correlation to be that of the blue (metal-poor) GC subpopulation and the dark matter content. This correlation implies that the dark matter mass of a galaxy can be estimated to within a factor of two from careful imaging of its GC system. The ratio of the GC system mass to that of the enclosed dark matter is nearly constant. We also find a strong correlation between the fraction of blue GCs and the fraction of enclosed dark matter, so that a typical galaxy with a blue GC fraction of 60 per cent has a dark matter fraction of 86 per cent over similar spatial scales. Both halo growth and removal (via tidal stripping) may play some role in shaping this trend. In the context of the two-phase model for galaxy formation, we find galaxies with the highest fractions of accreted stars to have higher dark matter fractions for a given fraction of blue GCs.