Globular Cluster Systems, Diffuse Star Clusters, and Host Galaxies in the ACS Virgo Cluster Survey

Abstract

We present the color distributions of globular cluster (GC) systems for 100 Virgo cluster early-type galaxies observed in the ACS Virgo Cluster Survey, the deepest and most homogeneous survey of this kind to date with over 11,000 observed GCs. On average, galaxies at all luminosities in our study (-22 < M_B < -15) appear to have bimodal or asymmetric GC color distributions. The colors of both subpopulations correlate with host galaxy luminosity and color, with the red GCs having a steeper slope. Using a preliminary nonlinear gz-[Fe/H] relation for globular clusters to convert color to metallicity, we find for the first time that the metallicities of metal-poor and metal-rich GCs vary similarly with respect to galaxy luminosity and stellar mass. We also present an investigation of the diffuse star cluster systems in the Virgo galaxies. Compared to globular clusters (GCs), these star clusters have moderately low luminosities (M_V>-8) and a broad distribution of sizes (3<r_h<30 pc), but they are principally characterized by their low mean surface brightnesses which can be more than three magnitudes fainter than a typical GC (μ_g >20 mag arcsec-2). These clusters are found in 12 galaxies, are typically red, and are largely found in lenticulars.