Exploring the Properties of the M31 Halo Globular Cluster System
  Following on from our discovery of a significant population of M31 outer halo
globular clusters (GCs), and updates to the Revised Bologna Catalogue of M31
GCs, we investigate the GC system of M31 out to an unprecedented radius
(~120kpc). We derive various ensemble properties, including the magnitude,
colour and metallicity distributions, as well as the GC number density profile.
One of our most significant findings is evidence for a flattening in the radial
GC number density profile in the outer halo. Intriguingly, this occurs at a
galactocentric radius of ~2 degrees (~30 kpc) which is the radius at which the
underlying stellar halo surface density has also been shown to flatten. The GCs
which lie beyond this radius are remarkably uniform in terms of their blue
(V-I)o colours, consistent with them belonging to an ancient population with
little to no metallicity gradient. Structural parameters are also derived for a
sample of 13 newly-discovered extended clusters (ECs) and we find the lowest
luminosity ECs have magnitudes and sizes similar to Palomar-type GCs in the
Milky Way halo. We argue that our findings provide strong support for a
scenario in which a significant fraction of the outer halo GC population of M31
has been accreted.
