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Session 115 - Star Clusters & Dwarf Galaxies.
Oral session, Saturday, January 10
Jefferson,
We compare the observed color and luminosity distributions of star cluster systems in the young merger remnants NGC 3921 and NGC 7252 with evolutionary models in order to investigate the shape of the mass function of young star clusters and the duration of cluster formation. The color distribution constrains the mean age of the young clusters and the period over which they formed. The mean ages are 350--550 Myr for NGC 3921 and 650--850 Myr for NGC 7252, while the burst durations are \lesssim400 Myr. None of our models with a lognormal mass function for the young clusters give good matches to the observations. However, models with a power-law mass function are good representations of the data.
This result has important implications for the question of whether young star clusters form by the same physical process as old globular clusters, which have lognormal mass functions. The differences may be due to how environmental conditions, including metallicity, affect the Jeans mass of cooling gas. Or, it may be that all clusters form from ``scale-free'' initial conditions and dynamical processes preferentially distrupt low mass clusters. More theoretical and observational work is being done to address these issues.
