Metallicity distribution of bulge globular clusters in M31

Abstract

This paper presents 3600—5400 Å integrated spectra of 19 globular clusters (or candidates) projected on the central regions of M31, r ≤ 5.3' ( ≈ 1.2 kpc). We check the cluster nature of these objects, and derive their ages, metallicities and reddenings. From the initial sample, 16 objects turn out to be true star clusters, two are Galactic dwarf stars, and one is a high redshift background galaxy. Only two clusters are found to be super metal-rich, suggesting that this phenomenon is not very common. For some clusters, we cannot rule out the possibility that they are of intermediate age; this requires confirmation by observations at the calcium triplet. We also present the metallicity histogram of this central bulge sample and discuss possible scenarios to explain its properties.