Evidence for an accretion origin for the outer halo globular cluster system of M31

TL;DR

This study provides strong evidence that most of the outer halo globular clusters in M31 originated from accreted satellite galaxies, based on their spatial correlation with stellar streams.

Contribution

It demonstrates a direct link between globular clusters and tidal streams in M31, supporting an accretion origin for these clusters.

Findings

Low probability (<1%) of chance alignment of clusters and streams.

Most outer halo globular clusters are associated with stellar debris.

Supports hierarchical galaxy formation models.

Abstract

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