The M31 globular cluster system: A view from the infrared

Abstract

Infrared photometry obtained with an array detector is presented for 23 globular clusters in M31, 16 of which have projected galactocentric radii of less than 1.1 kpc. A comparison with the metallicity determined for these objects by Huchra et al [ApJ, 370, 495 (1991)] using optical spectra indicates that the errors in [Fe/H] determined optically have been underestimated. Combining our sample with previously published infrared photometry of M31 globular clusters produces a total sample of 84 objects. A comparison of the properties of the M31 globular cluster system as viewed in the infrared with that of the Milky Way globular cluster system indicates that the two are very similar. The mean metallicity of the nuclear globular clusters in the two galaxies is the same to within 0.11 dex (29%), as is the mean metallicity of the globular clusters outside the nucleus in the two galaxies, which is within the uncertainties of the two〈[Fe/H]〉determinations. Aside from a general enhancement in metallicity in the nuclear sample in M31, there is no evidence among the outer globular clusters for a spatial gradient of metallicity in the M31 globular cluster sample. This, too, is in agreement with expectations based on what is observed in the Milky Way globular cluster system.

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