We present a new catalog of photometric and spectroscopic data on M31 globular clusters .
The catalog includes new optical and near-infrared photometry for a substantial fraction of the 435 clusters and cluster candidates .
We use these data to determine the reddening and intrinsic colors of individual clusters , and find that the extinction laws in the Galaxy and M31 are not significantly different .
There are significant ( up to 0.2 ^ { m } in V - K ) offsets between the clusters ’ intrinsic colors and simple stellar population colors predicted by population synthesis models ; we suggest that these are due to systematic errors in the models .
The distributions of M31 clusters ’ metallicities and metallicity-sensitive colors are bimodal , with peaks at { [ Fe / H ] } \approx - 1.4 and -0.6 .
The distribution of V - I is often bimodal in elliptical galaxies ’ globular cluster systems , but is not sensitive enough to metallicity to show bimodality in M31 and Galactic cluster systems .
The radial distribution and kinematics of the two M31 metallicity groups imply that they are analogs of the Galactic ‘ halo ’ and ‘ disk/bulge ’ cluster systems .
The globular clusters in M31 have a small radial metallicity gradient , suggesting that some dissipation occurred during the GCS formation .
The lack of correlation between cluster luminosity and metallicity in M31 GCs shows that self-enrichment is not important in GC formation .