An optical/NIR survey of globular clusters in early-type galaxies

Context. The interpretation that bimodal colour distributions of globular clusters (GCs) reflect bimodal metallicity distributions has been challenged. Non-linearities in the colour to metallicity conversions caused for example by the horizontal branch (HB) stars may be responsible for transforming...

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Bibliographic Details
Published in:	Astronomy and astrophysics (Berlin) 2012-03, Vol.539
Main Authors:	Chies-Santos, A. L., Larsen, S. S., Cantiello, M., Strader, J., Kuntschner, H., Wehner, E. M., Brodie, J. P.
Format:	Article
Language:	eng
Subjects:	galaxies: elliptical and lenticular galaxies: evolution galaxies: star clusters: general
Online Access:	Get full text
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Summary:	Context. The interpretation that bimodal colour distributions of globular clusters (GCs) reflect bimodal metallicity distributions has been challenged. Non-linearities in the colour to metallicity conversions caused for example by the horizontal branch (HB) stars may be responsible for transforming a unimodal metallicity distribution into a bimodal (optical) colour distribution. Aims. We study optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0 galaxies. Methods. We test whether the bimodal feature, generally present in optical colour distributions, remains in the optical/NIR ones. The latter colour combination is a better metallicity proxy than the former. We use KMM and GMM tests to quantify the probability that different colour distributions are better described by a bimodal, as opposed to a unimodal distribution. Results. We find that double-peaked colour distributions are more commonly seen in optical than in optical/NIR colours. For some of the galaxies where the optical (g − z) distribution is clearly bimodal, a bimodal distribution is not preferred over a unimodal one at a statistically significant level for the (g − K) and (z − K) distributions. The two most cluster-rich galaxies in our sample, NGC 4486 and NGC 4649, show some interesting differences. The (g − K) distribution of NGC 4649 is better described by a bimodal distribution, while this is true for the (g − K) distribution of NGC 4486 GCs only if restricted to a brighter sub-sample with small K-band errors (
ISSN:	0004-6361 1432-0746