The outer halo globular cluster system of M31 – I. The final PAndAS catalogue

Abstract

We report the discovery of 59 globular clusters (GCs) and two candidate GCs\nin a search of the halo of M31, primarily via visual inspection of CHFT/MegaCam\nimagery from the Pan-Andromeda Archaeological Survey (PAndAS). The superior\nquality of these data also allow us to check the classification of remote\nobjects in the Revised Bologna Catalogue (RBC), plus a subset of GC candidates\ndrawn from SDSS imaging. We identify three additional new GCs from the RBC, and\nconfirm the GC nature of 11 SDSS objects (8 of which appear independently in\nour remote halo catalogue); the remaining 188 candidates across both lists are\neither foreground stars or background galaxies. Our new catalogue represents\nthe first uniform census of GCs across the M31 halo - we find clusters to the\nlimit of the PAndAS survey area at projected radii of up to R_proj ~ 150 kpc.\nTests using artificial clusters reveal that detection incompleteness cuts in at\nluminosities below M_V = -6.0; our 50% completeness limit is M_V ~ -4.1. We\nconstruct a uniform set of PAndAS photometric measurements for all known GCs\noutside R_proj = 25$ kpc, and any new GCs within this radius. With these data\nwe update results from Huxor et al. (2011), investigating the luminosity\nfunction (LF), colours and effective radii of M31 GCs with a particular focus\non the remote halo. We find that the GCLF is clearly bimodal in the outer halo\n(R_proj > 30 kpc), with the secondary peak at M_V ~ -5.5. We argue that the GCs\nin this peak have most likely been accreted along with their host dwarf\ngalaxies. Notwithstanding, we also find, as in previous surveys, a substantial\nnumber of GCs with above-average luminosity in the outer M31 halo - a\npopulation with no clear counterpart in the Milky Way.\n