PHOTOMETRIC PROPERTIES OF THE M33 STAR CLUSTER SYSTEM

We present a catalog of 2990 extended sources in a 10 x 10 area centered on M33 using the MegaCam camera on the 3.6 m Canada-France-Hawaii Telescope. The catalog includes 599 new candidate stellar clusters, 204 previously confirmed clusters, 1969 likely background galaxies, and 218 unknown extended objects. We present ugriz integrated magnitudes of the candidates and confirmed star clusters (SCs) as well as the full width at half maximum, ellipticity, and stellarity. Based on the properties of the confirmed SCs, we select a sub-sample of highly probable clusters composed of 246 objects. The integrated photometry of the complete cluster catalog reveals a wide range of colors of -0.4 < (g - r) < 1.5 and -1.0 < (r - i) < 1.0 with no obvious cluster subpopulations. Comparisons with models of simple stellar populations suggest a large range of ages some as old as ∼10 Gyr. In addition, we find a sequence in the color-color diagrams that deviates from the expected direction of evolution. This feature could be associated with very young clusters (<107 yr) possessing significant nebular emission. Analysis of the radial density distribution suggests that the cluster system of M33 has suffered from significant depletion possibly due to interactions with M31. We also detect a gap in the cluster distribution in the color-color diagram at (g - r) ≅ 0.3 and (u - g) ≅ 0.8. This gap could be interpreted as an evolutionary effect. This complete catalog provides promising targets for deep photometry and high-resolution spectroscopy to study the structure and star formation history of M33.