Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy

Details Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy

2002-04-25

arxiv.org/abs/astro-ph/0204420v1

Astronomy and Astrophysics

Astrophysics

24 pages, including 9 figures and 3 tables. Accepted for publication in AJ

Scientific paper

10.1086/341389

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 metallicities 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 be ruled out. We also measure alpha-to-iron abundance ratios from Mg and TiO features and find enhancements on the order of +0.4 dex relative to the Sun, similar to the alpha/Fe abundance ratios observed in other old stellar populations. Finally, we combined our sample with radial velocities for 34 GCs from Bridges et al. 1997 and obtain virial and projected masses for the Sombrero of M(Vir) = 8.1+/-1.8 x 10^11 M(sun) and M(P) = 5.3+/-1.0 x 10^11 Msun within 17 kpc, respectively. Using 12 clusters within the central 4.5 kpc, the corresponding numbers are M(Vir) = 2.1+/-1.1 x 10^11 Msun and M(P) = 2.0+/-1.3 x 10^11 Msun.

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