A Semi-Analytic Approach to Understanding the Bimodality of GCs in the Milky Way & M31

One of the most important results in the study of Globular Cluster (GC) systems has been the discovery of bi-modality in both the broad-band colors and metallicity distributions of many systems. This has spawned competing theories of GC formation. One method of constraining, and perhaps better understanding the observed bi-modality of GCs is to use semi-analytic models (SAMs) to test both galaxy and GC formation scenarios. We present the results of a study to test whether SAMs can accurately reproduce the physical characteristics of both the parent galaxy (including luminosity, mass, and metallicity distribution of the stellar population) and GC populations. The focus of the work is to test whether the SAMs are capable of reproducing the observed properties of spiral galaxies, in particular, the Milky Way and M31, and what if any constraints this may place in the formation scenarios of GCs. Among the results are indications that bi-modality may be directly connected with reionization at z ∼ 7-8.