Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy 1

We analyze high signal-to-noise spectra for 14 globular clusters (GCs) in the Sombrero galaxy, NGC 4594 = M104, obtained with the LRIS spectrograph on the Keck I telescope. We find generally good agreement between spectroscopic metallicities and previous photometric metallicites based on V −I colors. Further, we use measurements of various Balmer line indices on co-added spectra of metal-poor and metal-rich GCs to estimate ages for the GC subpopulations and find ages of 10–15 Gyr, with preferred ages around 11–12 Gyr and no detectable differences between the metal-rich and metal-poor subpopulations. However, because of model and measurement uncertainties, age differences of a few (2–3) Gyrs cannot be ruled out. We also measure alpha to iron abundance ratios from Mg and TiO features and find enhancements on the order of [α/Fe] ∼ +0.4, similar to the [α/Fe] abundance ratios observed in other old stellar populations. Finally, we combine our sample with radial velocities for 34 GCs from Bridges et al. (1997) and obtain virial and projected masses for the Sombrero of MVT = (8.1 ± 1.8) × 10 11 M⊙ and MP = (5.3 ± 1.0) × 10 11 M⊙ within 17 kpc, respectively. Using 12 clusters within the central 4.5 kpc the corresponding numbers are MVT = (2.1 ± 1.1) × 10 11 M⊙ and MP = (2.0± 1.3) × 10 11 M⊙. Subject headings: galaxies: star clusters — galaxies: abundances – galaxies: halos — galaxies: bulges — galaxies: individual (NGC 4594) Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.