The Globular Cluster Systems of Abell 1185

TL;DR

This study investigates a population of globular clusters in Abell 1185, finding most are likely intergalactic rather than bound to individual galaxies, highlighting the need for further observations to determine their true nature.

Contribution

It provides the first detailed analysis suggesting a predominantly intergalactic origin for globular clusters in a galaxy cluster core.

Findings

Approximately 1300 globular clusters detected.

Most clusters are likely intergalactic, not bound to any galaxy.

Colors and luminosities resemble metal-poor globulars in galaxies.

Abstract

We examine the properties of a previously discovered population of globular clusters in the heart of the rich galaxy cluster Abell 1185 that might be intergalactic in nature. Deep images obtained with the Advanced Camera for Surveys (ACS) aboard Hubble Space Telescope (HST) confirm the presence of ~ 1300 globular clusters brighter than I_{F814W} = 27.3 mag in a field devoid of any large galaxies. The luminosities and colors of these objects are found to be similar to those of metal-poor globular clusters observed in many galaxies to date. Although a significant fraction of the detected globular clusters undoubtedly reside in the outer halos of galaxies adjacent to this field, detailed modeling of their distribution suggests that the majority of these objects are likely to be intergalactic, in the sense that they are not gravitationally bound to any individual galaxy. We conclude that the true nature and origin of the globular cluster population in the core of A1185 -- galactic residents or intergalactic wanderers -- remains uncertain, and suggest how future observation could resolve this ambiguity.