Spectral energy distributions and age estimates of 39 globular clusters in M31

Abstract

This paper supplements Jiang et al., who studied 172 M31 globular clusters (GCs) and GC candidates from Battistini et al. on the basis of integrated photometric measurements in the Beijing-Arizona-Taiwan-Connecticut (BATC) photometric system. Here, we present multicolor photometric CCD data (in the BATC system) for the remaining 39 M31 GCs and candidates. In addition, the ages of 35 GCs are constrained by comparing our accurate photometry with updated theoretical stellar synthesis models. We use photometric measurements from the Galaxy Evolution Explorer in the far- and near-ultraviolet and Two Micron All Sky Survey infrared JHKs data, in combination with optical photometry. Except for two clusters, the ages of the other sample GCs are all older than 1 Gyr. Their age distribution shows that most sample clusters are younger than 6 Gyr, with a peak at ∼3 Gyr, although the "usual" complement of well-known old GCs (i.e., GCs of similar age as the majority of the Galactic GCs) is present as well. © 2009. The American Astronomical Society. All rights reserved.