The formation and early dynamical evolution of bound stellar systems

The authors present the results of numerical N-body calculations which simulate the dynamical evolution of young clusters as they emerge from molecular clouds. They follow the evolution of initially virialized stellar systems of 50 and, in some cases, 100 stars from the point in time immediately after the stars have formed in a cloud until a time long after all the residual star-forming gas has been dispersed from the system. It is found that clusters which remain bound after gas dispersal undergo significant expansion as they emerge from a cloud and in the process may lose 10% - 80% of their stars, depending on the star formation efficiency at the time of gas removal and duration of gas removal from the system. By scaling the models to match the observed parameters of real clusters the authors constrain the range of initial mass densities, sizes, and velocity dispersions of protocluster molecular clouds. Arguments are presented which suggest that even if a newly formed stellar system was not initially virialized, it would most likely reach such an equilibrium state before significant gas removal occurred.