Dynamical masses of young star clusters: Constraints on the stellar IMF and star formation efficiency

Through the use of detailed light profiles and dynamical measurements of young clusters we investigate claims that the stellar initial mass function (IMF) within clusters varies greatly. We find a strong age dependence in the clusters which have been claimed to have non-standard stellar IMFs, and suggest that the lack of equilibrium of these clusters is responsible for their "strange" light-to-mass ratios and not IMF variations. The most likely culprit is the rapid removal of residual gas left over from the star formation process, which leaves the clusters severely out of dynamical equilibrium. By comparing the observations to N-body simulations we quantify to what degree a cluster is out of equilibrium and consequently its survival chances. We find that > 60% of young clusters will be disrupted, due to gas removal, within the first 20-50 Myr of their lives.