We present the color distributions of globular cluster (GC) systems for 100 Virgo cluster early-type galaxies observed in the ACS Virgo Cluster Survey, the deepest and most homogeneous survey of this kind to date. While the color distributions of individual GC systems can show significant variations from one another, their general properties are consistent with continuous trends across galaxy luminosity, color, and stellar mass. 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%. The colors of both subpopulations correlate with host galaxy luminosity and color, with the red GCs having a steeper slope. The steeper correlation seen in the mean color of the entire GC system is driven by the increasing fraction of metal-rich GCs for more luminous galaxies. To convert color to metallicity, we also 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 mass-metallicity relation for star forming galaxies in the same mass range. The offset between the two GC populations varies slowly (∝ M0.05) and is approximately 1 dex across three 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.

Publication Date



This is the pre-print of an article published by the American Astronomical Society. The final, published version is available here: https://doi.org/10.1086/498210

© 2006 The American Astronomical Society

Also archived in: arXiv: astro-ph/0509654 v1 22 Sep 2005

EP thanks C. Tremonti for useful discussions on the mass-metallicity relation. Support for program GO-9401 was provided through a grant from the Space Telescope Science Institute, which is operated by the Association for Research in Astronomy, Inc., under NASA contract NAS5-26555. Partial support for this work was provided by NASA LTSA grant NAG5-11714 to PC. M. J.W. acknowledges support through NSF grant AST 02-05960. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Cen- ter/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Facilities: HST(ACS), CTIO.ISSN:1538-4357

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School of Physics and Astronomy (COS)


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