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