Star Cluster Formation and Destruction in the Merging Galaxy NGC 3256

Abstract: We use the Advanced Camera for Surveys on the Hubble Space Telescope to study the rich population of young massive star clusters in the main body of NGC 3256, a merging pair of galaxies with a high star formation rate (SFR) and SFR per unit area ($\Sigma_{\rm{SFR}}$). These clusters have luminosity and mass functions that follow power laws, $dN/dL \propto L^{\alpha}$ with $\alpha = -2.23 \pm 0.07$, and $dN/dM \propto M^{\beta}$ with $\beta = -1.86 \pm 0.34$ for $\tau < 10$ Myr clusters, similar to those found in more quiescent galaxies. The age distribution can be described by $dN/d\tau \propto \tau ^ \gamma$, with $\gamma \approx -0.67 \pm 0.08$ for clusters younger than about a few hundred million years, with no obvious dependence on cluster mass. This is consistent with a picture where $\sim 80 \%$ of the clusters are disrupted each decade in time. We investigate the claim that galaxies with high $\Sigma_{\rm{SFR}}$ form clusters more efficiently than quiescent systems by determining the fraction of stars in bound clusters ($\Gamma$) and the CMF/SFR statistic (CMF is the cluster mass function) for NGC 3256 and comparing the results with those for other galaxies. We find that the CMF/SFR statistic for NGC 3256 agrees well with that found for galaxies with $\Sigma_{\rm{SFR}}$ and SFRs that are lower by $1-3$ orders of magnitude, but that estimates for $\Gamma$ are only robust when the same sets of assumptions are applied. Currently, $\Gamma$ values available in the literature have used different sets of assumptions, making it more difficult to compare the results between galaxies.