Testing stellar population synthesis models with Sloan Digital Sky
  Survey colors of M31's globular clusters
  Accurate stellar population synthesis models are vital in understanding the
properties and formation histories of galaxies. In order to calibrate and test
the reliability of these models, they are often compared with observations of
star clusters. However, relatively little work has compared these models in the
ugriz filters, despite the recent widespread use of this filter set. In this
paper, we compare the integrated colors of globular clusters in the Sloan
Digital Sky Survey (SDSS) with those predicted from commonly used simple
stellar population (SSP) models. The colors are based on SDSS observations of
M31's clusters and provide the largest population of star clusters with
accurate photometry available from the survey. As such, it is a unique sample
with which to compare SSP models with SDSS observations. From this work, we
identify a significant offset between the SSP models and the clusters' g-r
colors, with the models predicting colors which are too red by g-r\sim0.1. This
finding is consistent with previous observations of luminous red galaxies in
the SDSS, which show a similar discrepancy. The identification of this offset
in globular clusters suggests that it is very unlikely to be due to a minority
population of young stars. The recently updated SSP model of Maraston &
Stromback better represents the observed g-r colors. This model is based on the
empirical MILES stellar library, rather than theoretical libraries, suggesting
an explanation for the g-r discrepancy.
