The ACS Virgo Cluster Survey. IX. The Color Distributions of Globular Cluster Systems in Early-Type Galaxies
Abstract
We present the color distributions of globular cluster (GC) systems for 100 early-type galaxies observed in the ACS Virgo Cluster Survey, the deepest and most homogeneous survey of this kind to date. On average, galaxies at all luminosities in our study (-22<MB<-15) appear to have bimodal or asymmetric GC color distributions. Almost all galaxies possess a component of metal-poor GCs, with the average fraction of metal-rich GCs ranging from 15% to 60% and increasing with luminosity. The colors of both subpopulations correlate with host galaxy luminosity and color, with the red GCs having a steeper slope. To convert color to metallicity, we introduce a preliminary (g-z)-[Fe/H] relation calibrated to Galactic, M49, and M87 GCs. This relation is nonlinear, with a steeper slope for [Fe/H]<~-0.8. As a result, the metallicities of the metal-poor and metal-rich GCs vary similarly with respect to galaxy luminosity and stellar mass, with relations of [Fe/H]MP~L0.16+/-0.04~M0.17+/-0.04* and [Fe/H]MR~L0.26+/-0.03~M0.22+/-0.03*, respectively. Although these relations are shallower than the mass-metallicity relation predicted by wind models and observed for dwarf galaxies, they are very similar to the relation observed for star-forming galaxies in the same mass range. The offset between the two GC populations is approximately 1 dex across 3 orders of magnitude in mass, suggesting a nearly universal amount of enrichment between the formation of the two populations of GCs. We also find that although the metal-rich GCs show a larger dispersion in color, it is the metal-poor GCs that have an equal or larger dispersion in metallicity. The similarity in the M*-[Fe/H] relations for the two populations implies that the conditions of GC formation for metal-poor and metal-rich GCs could not have been too different. Like the color-magnitude relation, these relations derived from globular clusters present stringent constraints on the formation and evolution of early-type galaxies.
Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2006
- DOI:
- 10.1086/498210
- arXiv:
- arXiv:astro-ph/0509654
- Bibcode:
- 2006ApJ...639...95P
- Keywords:
-
- Galaxies: Elliptical and Lenticular;
- cD;
- Galaxies: Evolution;
- Galaxies: Star Clusters;
- Galaxy: Globular Clusters: General;
- Astrophysics
- E-Print:
- 25 pages, 16 figures, 7 tables. Accepted for publication in the Astrophysical Journal. Version with Figures 1,5-9,11-16 in color is available at http://www.physics.rutgers.edu/~pcote/acs/acsvcs_9.pdf