The correlation between the sizes of globular cluster systems and their
  host dark matter haloes
  The sizes of entire systems of globular clusters (GCs) depend on the
formation and destruction histories of the GCs themselves, but also on the
assembly, merger and accretion history of the dark matter (DM) haloes that they
inhabit. Recent work has shown a linear relation between total mass of globular
clusters in the globular cluster system and the mass of its host dark matter
halo, calibrated from weak lensing. Here we extend this to GC system sizes, by
studying the radial density profiles of GCs around galaxies in nearby galaxy
groups. We find that radial density profiles of the GC systems are well fit
with a de Vaucouleurs profile. Combining our results with those from the
literature, we find tight relationship ($\sim 0.2$ dex scatter) between the
effective radius of the GC system and the virial radius (or mass) of its host
DM halo. The steep non-linear dependence of this relationship ($R_{e, GCS}
\propto R_{200}^{2.5 - 3}$) is currently not well understood, but is an
important clue regarding the assembly history of DM haloes and of the GC
systems that they host.
