A Search for Intergalactic Globular Clusters in the Local Group

Abstract

The whole Sloan Digital Sky Survey (SDSS, 14,555 {{deg }²}) has been searched for intergalactic globular clusters (IGCs) in the Local Group (LG). Using optical, infrared, and ultraviolet photometric selection criteria and photometric redshifts, the 2.1× {{10}⁸} objects in the SDSS Galaxy Catalog were reduced to only 183,791 brighter than {{r}₀}=19 that might be GCs. Visual examination of their SDSS images recovered 84% of the confirmed GCs in M31 and M33 and yielded 17 new GC candidates, 5 of them of high confidence, which we could confirm as GCs in MegaPrime images from the Canada-France-Hawaii Telescope. These 5 GCs are within M31's halo, but the other 12 candidates are not close to LG galaxies or galaxies within 3 Mpc of the LG. Even though this search covers only one-third of the sky and some GCs could have been missed, it suggests that the LG does not contain a large population of IGCs more luminous than {{M}_V}∼ -6. In the direction of the M81 Group, the search yielded five candidate GCs, probable members of that group.