Globular Cluster Populations: Signatures and Implications

Abstract

The formation of populous secondary star cluster systems is a widespread phenomenon in mergers of gas-rich galaxies. Many, if not most, of those clusters are massive and compact enough to be young globular clusters (GCs). GC systems in most E/S0 galaxies feature bimodal color distributions with a fairly universal blue peak similar to the blue peak of halo GCs in the Milky Way (MW) and M31, and a variable red peak. Due to the well-known age -- metallicity degeneracy of optical broad-band colors, the metallicities and ages, and, hence, the origin of the red peak GCs are not yet known. We use evolutionary synthesis models for GC {\bf systems} of various metallicities to study the time evolution of their luminosity functions (LFs) in various bands U,..., K and of their color distributions. By comparison with the universal blue peak GC population we investigate for which combinations of age and metallicity a second GC population can or cannot be identified in typical observations of GC color distributions and we discuss implications for the GC LF as a distance indicator.