The Age Distribution of Massive Star Clusters in the Antennae Galaxies

We determine the age distribution of star clusters in the Antennae galaxies(NGC 4038/9) for two mass-limited samples (M > 3 x 10^4 M_{\odot} and M > 2 x10^5 M_{\odot}). This is based on integrated broadband UBVI and narrowbandH-alpha photometry from deep images taken with the Hubble Space Telescope. Wefind that the age distribution of the clusters declines steeply, approximatelyas dN/d\tau \propto \tau^{-1}. The median age of the clusters is ~10^7 yr,which we interpret as evidence for rapid disruption ("infant mortality"). It isvery likely that most of the young clusters are not gravitationally bound andwere disrupted near the times they formed by the energy and momentum input fromyoung stars to the interstellar matter of the protoclusters. At least 20% andpossibly all stars form in clusters and/or associations, including those thatare unbound and short-lived.Comment: 11 pages, 2 figures. To appear in the ApJ Letters; Submitted 2004 July 29; accepted 2005 August