Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters

We present new (B, I) photometry for the globular cluster systems in eight brightest cluster galaxies (BCGs), obtained with the ACS/WFC camera on the Hubble Space Telescope. In the very rich cluster systems that reside within these giant galaxies, we find that all have strongly bimodal color distributions that are clearly resolved by the metallicity-sensitive (B - I) index. Furthermore, the mean colors and internal color range of the blue …