Photometric Properties of the M33 Star Cluster System
  We present a catalog of 2,990 extended sources in a 1deg x1deg area centered
on M33 using the MegaCam camera on the 3.6m Canada-France-Hawaii telescope
(CFHT). The catalog includes 599 new candidate stellar clusters, 204 previously
confirmed clusters, 1,969 likely background galaxies and 218 unknown extended
objects. We present ugriz integrated magnitudes of the candidates and confirmed
star clusters as well as full width at half maximum, ellipticity and
stellarity. Based on the properties of the confirmed star clusters, 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 from
-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 Gyrs. 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 (< 10^7
yrs) 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.
