THE LUMINOSITY, MASS, AND AGE DISTRIBUTIONS OF COMPACT STAR CLUSTERS IN M83 BASED ON<i>HUBBLE SPACE TELESCOPE</i>/WIDE FIELD CAMERA 3 OBSERVATIONS

Abstract

The newly installed Wide Field Camera 3 (WFC3) on the Hubble Space Telescope\nhas been used to obtain multi-band images of the nearby spiral galaxy M83.\nThese new observations are the deepest and highest resolution images ever taken\nof a grand-design spiral, particularly in the near ultraviolet, and allow us to\nbetter differentiate compact star clusters from individual stars and to measure\nthe luminosities of even faint clusters in the U band. We find that the\nluminosity function for clusters outside of the very crowded starburst nucleus\ncan be approximated by a power law, dN/dL \\propto L^{alpha}, with alpha = -2.04\n+/- 0.08, down to M_V ~ -5.5. We test the sensitivity of the luminosity\nfunction to different selection techniques, filters, binning, and aperture\ncorrection determinations, and find that none of these contribute significantly\nto uncertainties in alpha. We estimate ages and masses for the clusters by\ncomparing their measured UBVI,Halpha colors with predictions from single\nstellar population models. The age distribution of the clusters can be\napproximated by a power-law, dN/dt propto t^{gamma}, with gamma=-0.9 +/- 0.2,\nfor M &gt; few x 10^3 Msun and t &lt; 4x10^8 yr. This indicates that clusters are\ndisrupted quickly, with ~80-90% disrupted each decade in age over this time.\nThe mass function of clusters over the same M-t range is a power law, dN/dM\npropto M^{beta}, with beta=-1.94 +/- 0.16, and does not have bends or show\ncurvature at either high or low masses. Therefore, we do not find evidence for\na physical upper mass limit, M_C, or for the earlier disruption of lower mass\nclusters when compared with higher mass clusters, i.e. mass-dependent\ndisruption. We briefly discuss these implications for the formation and\ndisruption of the clusters.\n