Gas expulsion in massive star clusters?: Constraints from observations of young and gas-free objects

Gas expulsion is a central concept in some of the models for multiple populations and the light-element anti-correlations in globular clusters. We investigate the conditions required for residual gas expulsion on the crossing timescale. We consider a standard initial mass function and different models for the energy production in the cluster: metallicity-dependent stellar winds, radiation, supernovae and more energetic events, such as hypernovae, which are related to gamma ray bursts. The latter may be more energetic than supernovae by up to two orders of magnitude. We computed a large number of thin-shell models for the gas dynamics, and calculated whether the Rayleigh-Taylor instability is able to disrupt the shell before it reaches the escape speed. Globular clusters should initially have C5 100, if the gas expulsion paradigm was correct. Most likely, the stellar masses did not change significantly at the removal of the primordial gas. On this basis, compact young massive clusters should also have multiple populations.