EVIDENCE FOR AN ACCRETION ORIGIN FOR THE OUTER HALO GLOBULAR CLUSTER SYSTEM OF M31

Abstract

We use a sample of newly-discovered globular clusters from the Pan-Andromeda\nArchaeological Survey (PAndAS) in combination with previously-catalogued\nobjects to map the spatial distribution of globular clusters in the M31 halo.\nAt projected radii beyond ~30 kpc, where large coherent stellar streams are\nreadily distinguished in the field, there is a striking correlation between\nthese features and the positions of the globular clusters. Adopting a simple\nMonte Carlo approach, we test the significance of this association by computing\nthe probability that it could be due to the chance alignment of globular\nclusters smoothly distributed in the M31 halo. We find the likelihood of this\npossibility is low, below 1%, and conclude that the observed spatial\ncoincidence between globular clusters and multiple tidal debris streams in the\nouter halo of M31 reflects a genuine physical association. Our results imply\nthat the majority of the remote globular cluster system of M31 has been\nassembled as a consequence of the accretion of cluster-bearing satellite\ngalaxies. This constitutes the most direct evidence to date that the outer halo\nglobular cluster populations in some galaxies are largely accreted.\n