More Remote Globular Clusters in the Outer Halo of M31

TL;DR

This study used SDSS data to discover 18 new globular clusters around M31, including six in the outer halo beyond 100 kpc, expanding knowledge of M31's remote halo structure.

Contribution

It reports the discovery of new globular clusters in M31's outer halo, including the farthest known cluster at 158 kpc, using a large-scale survey and visual inspection.

Findings

Identified 18 new globular clusters around M31.

Discovered 6 clusters beyond 100 kpc, with the farthest at 158 kpc.

Survey covered approximately 200 square degrees.

Abstract

We searched the Sloan Digital Sky Survey for outer halo globular clusters (GCs) around M31. Our search of non-stellar objects, within the limits 0.3 < (g-i)o < 1.5 and 14.0 < ro < 19.0 concentrated in some remote areas of the extended halo, to a maximum projected distance of 240 kpc, for a total of approximately 200 square degrees. Another roughly 50 square degrees, approximately 5-75 kpc from M31, were surveyed as test areas. In these areas, we identified 39 GCs and 2 GC candidates, 84% of the previously known GCs (93% of the "classical GCs" and 40% of the "halo extended clusters", on the cluster classification scheme of Huxor et al.). For the entire survey, we visually inspected 78,516 objects for morphological evidence of cluster status, and we identified 18 new clusters, and 75 candidate clusters. The new clusters include 15 classical globulars and three clusters of lower density. Six of the clusters reside in the remote areas of the outer halo, beyond projected distances of 100 kpc. Previously, only MGC1 was found beyond this limit at 117 kpc. The farthest cluster discovered in this survey lies at a projected radius of 158 kpc from M31, assuming that the M31 distance is 780 kpc.