SED, metallicity and age of halo globular clusters in M 33

Abstract

In this paper we study the properties of ten halo globular clusters in the nearby spiral galaxy M 33. CCD images of M 33 were obtained as a part of the BATC Colour Survey of the sky in 13 intermediate-band filters from 3800 to 10 000 Å. By aperture photometry, we obtain the spectral energy distributions (SEDs) of these globular clusters. We estimate the ages of our sample clusters by comparing the photometry of each object with theoretical stellar population synthesis models for different values of metallicity. Our results suggest that eight of the ten sample halo globular clusters have "intermediate" ages, i.e. between 1 and 8 Gyrs.