Near-infrared observations of globular clusters in NGC 4472, NGC 4594, NGC 3585, and NGC 5813 and implications for their ages and metallicities

Hempel, M., Zepf, S., Kundu, A., Geisler, D. and Maccarone, T.J. (2007) Near-infrared observations of globular clusters in NGC 4472, NGC 4594, NGC 3585, and NGC 5813 and implications for their ages and metallicities. The Astrophysical Journal, 661 (2), 768-778. (doi:10.1086/514808).

Abstract

We present near-infrared photometry of the globular cluster systems of the early-type galaxies NGC 4472, NGC 4594, NGC 3585, and NGC 5813. We combine these near-infrared data, obtained with PANIC at the Magellan Baade 6.5 m telescope, with archival optical HST and FORS/VLT data, and use the optical to near-infrared colors to constrain the ages and metallicities of the globular clusters around the target galaxies. For NGC 4472 we have the most extensive near-infrared and optical photometric data set. These colors show that the NGC 4472 globular cluster system has a broad metallicity distribution and that the clusters are predominantly old (i.e., ages of about 10 Gyr or more). This result agrees well with earlier spectroscopic work on NGC 4472, and is evidence that the combination of optical to near-infrared colors can identify predominantly old systems and distinguish these from systems with a substantial intermediate-age component. Based on the smaller sample of combined optical and near-infrared data, NGC 4594 and NGC 3585 appear to have predominantly old globular cluster systems, while that of NGC 5813 may have a more significant age spread. We also match our sample of globular clusters with near-infrared and optical photometry to Chandra X-ray source detections in these galaxies, and discuss how the probability that a globular cluster hosts a low-mass X-ray binary depends on metallicity and age

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