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A. Kundu, S. Zepf (Michigan State University), K. Ashman (U Kansas/ Baker University)
Observations of the globular cluster systems of a wide variety of galaxies reveal that the globular cluster luminosity function (GCLF) of old cluster systems has a characteristic Gaussian shape with a nearly constant turnover magnitude everywhere. Young cluster systems in merging galaxies on the other hand appear to have power law luminosity distributions with no obvious turnover at the expected magnitude. It is believed that various cluster destruction mechanisms erode an initial power law distribution to the present-day Gaussian shape. However there has been no convincing observational test of the viability of the various competing destruction forces (evaporation by internal relaxation, tidal shocks, dynamical friction, etc.) to date.
Theories of cluster destruction mechanisms make specific predictions about the radial variations in the properties of the GCLF. We present a comprehensive global analysis of the M87 globular cluster system using archival HST data that allows us to accurately determine the parameters of the GCLF continuously from the core of the galaxy out to a galactocentric radius of 75 Kpc. By virtue of the very large database of observations and the richness of the M87 globular cluster system, our analysis provides an observational sample that it at least an order of magnitude more sensitive to radial changes in the GCLF than existing data sets. We compare our observations to the predictions of the competing theoretical models of destruction mechanisms and comment on their viability.
Support for this work was provided by NASA through grant number HST-AR-09208.01-A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.