Astrophysics, abstract
astro-ph/0606419

From: Thomas H. Puzia [view email]

Date: Mon, 19 Jun 2006 17:49:23 GMT (98kb)

A Genuine Intermediate-Age Globular Cluster in M33

Authors: Rupali Chandar (1), Thomas H. Puzia (2), Ata Sarajedini (3), Paul Goudfrooij (2) (1 - Johns Hopkins University, 2 - STScI, 3 - University of Florida)

Comments: 4 pages, 3 figures, accepted for publication in ApJ Letters

Report-no: STScI Eprint #1725

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.

http://arxiv.org/abs/astro-ph/0606419