The Ages and Abundances of a Sample of Globular Clusters in M49 (NGC 4472)

We present a study of the metallicity and age of the globular clusters systemof M49 (NGC 4472), the most luminous galaxy in the Virgo cluster. We measureLick indices for 47 GCs in M49 from LRIS/Keck spectra and establish theirmetallicity parameters qualitatively in comparison to the Galactic GCs and topublished data for 150 M87 GCs. We then compare our measurements with thepredictions of models for the integrated light of old single burst stellarsystems by Worthey and by Thomas, Maraston & Bender. We find that themetallicity of the M49 GC system spans the range from [Fe/H]_Z = -2.0 to +0.4dex. We show that the metallicity and age parameters for these two GC systemsare basically identical, except that the M49 GCs reach slightly highermetallicities than do those of M87. We find that the GCs of both of these giantelliptical galaxies are alpha-enhanced by a factor of about two above the Solarvalue, as is also true of the Galactic GCs. While adoption of thealpha-enhanced models of TMB has eliminated most of the previous discrepancieswith observations, the most metal rich M49 GCs have NaD lines which are stillconsiderably stronger than those predicted by any model, and there are stillissues involving the metallicity scale of these models. We find that in themean, the M49 GCs are at least 10 Gyr old. However, the grids of models we useddiffer in how they treat the horizontal branch, and this perceptibly affectsthe predicted Hbeta index. Hence our current incomplete understanding of therole of the horizontal branch limits our ability to derive a more detaileddistribution for the ages of the GCs in M49 and in M87.Comment: Accepted to the Ap