Program: GN-2007B-Q-58

Globular clusters play a vital role as probes of galaxy formation and evolution. We recently demonstrated that M31 possesses a population of remote halo clusters which possess properties quite unlike those of the most remote Galactic globulars. We have discovered a new luminous globular cluster, at projected radius ~116kpc. Its true distance from M31 may be ~175kpc, making it the most remote known M31 member, and the most isolated known cluster in the Local Group. Surprisingly, it appears rather metal-rich compared with other outer-halo M31 globulars. We propose deep three-colour imaging of this object, in order to precisely constrain its distance, metallicity, and horizontal-branch-morphology, and hence accurately assess its position within the M31 halo. These measurements will allow us to further investigate the properties of the remote halo cluster population of M31 compared with that in the Milky Way, with implications for the assembly histories of the two galaxies.