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Q. Zhang (JHU/STScI), S. M. Fall, B. C. Whitmore (STScI)
We present new results from our study of young star clusters in the merging galaxy NGC 4038/9 ("the Antennae" galaxies). With the high-resolution HST WFPC2 observations, we obtained a large sample of star clusters located in the central disks of NGC 4038/9. The clusters formed during the merging process and have a variety of ages ranging from a few to several hundred million years. The young star clusters have properties that are consistent with old globular clusters (e.g., their mass and size). However, we find that both their luminosity function and their mass function are, to first order, described by power-laws with indices close to -2, rather than bell-shaped distributions appropriate for old globular clusters. We construct simple and largely analytical models to explore the evolutionary connection between the young star clusters and old globular clusters. We compute the effects of disruption on the mass function, including evaporation by two-body relaxation, disk shocks, and mass loss by stellar evolution. We find that for a wide variety of initial conditions the mass function develops a turnover or peak, and that after 12 Gyr the distribution is remarkably close to the observed peak for old globular clusters (i.e. MV=-7.2 mag and M=2 105 solar masses). Finally, we explore the relationship between the positions of the young star clusters in the Antennae and the properties of the interstellar medium, as defined by both intensity maps (covering a range of wavelengths from X-rays to radio waves) and velocity fields (from H-alpha, CO, and HI). Support for this work is provided in part by NASA through grant number GO-07468 from STScI.