Bibcode
DOI
Larsen, Søren S.; Brodie, Jean P.; Beasley, Michael A.; Forbes, Duncan A.
Bibliographical reference
The Astronomical Journal, Volume 124, Issue 2, pp. 828-838.
Advertised on:
8
2002
Citations
39
Refereed citations
32
Description
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) gigayears cannot be ruled out. We also measure
α-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. and obtain virial and projected masses for the Sombrero
of MVT=(8.1+/-1.8)×1011 Msolar
and MP=(5.3+/-1.0)×1011 Msolar
within 17 kpc, respectively. Using 12 clusters within the central 4.5
kpc the corresponding numbers are MVT=(2.1+/-1.
1)×1011 Msolar and
MP=(2.0+/-1.3)×1011 Msolar. 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. The Observatory was made possible by the generous
financial support of the W. M. Keck Foundation.