M31 globular clusters: colors and metallicities

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Title: M31 globular clusters: colors and metallicities
Author(s): Barmby, Pauline; Huchra, John P.; Brodie, Jean P.; Forbes, Duncan A.; Schroder, Linda L.; Grillmair, Carl J.
Abstract: We present a new catalog of photometric and spectroscopic data on M31 globular clusters (GCs). The catalog includes new optical and near-infrared photometry for a substantial fraction of the 435 clusters and cluster candidates. We use these data to determine the reddening and intrinsic colors of individual clusters, and we find that the extinction laws in the Galaxy and M31 are not significantly different. There are significant (up to 0.2 mag in V-K) offsets between the clusters' intrinsic colors and simple stellar population colors predicted by population synthesis models; we suggest that these are due to systematic errors in the models. The distributions of M31 clusters' metallicities and metallicity-sensitive colors are bimodal, with peaks at [Fe/H] approx -1.4 and -0.6. The distribution of V-I is often bimodal in elliptical galaxies' globular cluster systems, but it is not sensitive enough to metallicity to show bimodality in M31 and Galactic cluster systems. The radial distribution and kinematics of the two M31 metallicity groups imply that they are analogs of the Galactic 'halo' and 'disk/bulge' cluster systems. The globular clusters in M31 have a small radial metallicity gradient, suggesting that some dissipation occurred during the formation of the globular cluster system. The lack of correlation between cluster luminosity and metallicity in M31 GCs shows that self-enrichment is not important in GC formation.
Publication type: Journal article
Source: Astronomical Journal, Vol. 119, no. 2 (Feb 2000), pp. 727-747
Publication year: 2000
Keyword(s): Galaxies; Globular clusters; M31; Star clusters
Publisher: University of Chicago Press
ISSN: 0004-6256
Publisher URL: http://dx.doi.org/10.1086/301213
Additional information: Work reported here based on observations made with the Multiple Mirror Telescope, a joint facility of the Smithsonian Institution and the University of Arizona. Some of the data presented herein were 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 support of the W. M. Keck Foundation. 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 Center, funded by the National Aeronautics and Space Administration and the National Science Foundation.
Peer reviewed