A Genuine Intermediate-Age Globular Cluster in M33
Abstract
We present deep integrated-light spectroscopy of nine M33 globular clusters taken with the Hectospec instrument at the MMT Observatory. Based on our spectroscopy and previous deep color-magnitude diagrams obtained with HST/WFPC2, we present evidence for the presence of a genuine intermediate-age globular cluster in M33. The analysis of Lick line indices indicates that all globular clusters are metal-poor ([Z/H] <~ -1.0) and that cluster M33-C38 is about 5-8 Gyr younger than the rest of the sample M33 star clusters. We find no evidence for a population of blue horizontal branch stars in the CMD of M33-C38, which rules out the possibility of an artificially young spectroscopic age due to the presence of hot stars. We infer a total mass of 5-9 x 10^4 M_sol for M33-C38, which implies that M33-C38 has survived ~2-3 times longer than some dynamical evolution model predictions for star clusters in M33, although it is not yet clear to which dynamical component of M33 - thin disk, thick disk, halo - the cluster is associated.
Cite
@article{arxiv.astro-ph/0606419,
title = {A Genuine Intermediate-Age Globular Cluster in M33},
author = {Rupali Chandar and Thomas H. Puzia and Ata Sarajedini and Paul Goudfrooij},
journal= {arXiv preprint arXiv:astro-ph/0606419},
year = {2009}
}
Comments
4 pages, 3 figures, accepted for publication in ApJ Letters