A Point-Source Excess in Abell 1185: Intergalactic Globular Clusters?

Deep imaging with WFPC2 and the Hubble Space Telescope has been used to search for a population of intergalactic globular clusters (GCs) belonging to A1185, a richness class I cluster at cz = 9800 km s-1. The field is noteworthy in that contains no bright galaxies and yet is centered on the peak of the cluster's X-ray surface brightness distribution. We detect a total of 99 point sources in this field to a limiting magnitude of IF814W ≃ 26. An identical analysis of the Hubble Deep Field North, which serves as our control field, reveals a total of 12 objects in the same magnitude range. We discuss possible explanations for this discrepancy and conclude that the point source excess is likely due to the presence of GCs within A1185. The number and spatial distributions of these GCs are consistent with their being intergalactic in nature, although we cannot rule out the possibility that some of the GCs may be associated with neighboring bright galaxies. Deeper imaging with the Advanced Camera for Surveys may resolve this ambiguity.