RESIDUAL-GAS EXPULSION FROM YOUNG GLOBULAR-CLUSTERS

The results of N-body simulations of the effects of the expulsion of r esidual gas (that gas not used in star formation) from very young glob ular clusters is presented. Globular clusters of a variety of initial masses, Galactocentric radii, concentration and initial mass function slope with star formation efficiencies of less than or similar to 50 p er cent were simulated. The residual gas was expelled by the action of massive stars in one of three idealized ways: gradually by their UV f lux and stellar winds; gradually by the input of energy by supernovae; and in a 'supershell' expanding from the cluster centre. The clusters were compared shortly after the gas expulsion with the results of Che rnoff & Shapiro to estimate whether they would survive for a Hubble ti me. It is found that the expulsion of greater than or similar to 50 pe r cent of a globular cluster's mass in a short period of time consider ably affects the structure of the cluster. However, many clusters are estimated to be able to survive with reasonable initial conditions, ev en if their star formation efficiencies are possibly as low as 20 per cent. It is found that the central density required within a proto-glo bular cluster at star formation in order for it to survive at a given Galactocentric radius is independent of the mass of stars in the clust er. For globular clusters in the inner few kpc of the Galaxy this valu e is found to be around 10(3) M(circle dot) pc(-3), falling as Galacto centric radius increases. This value is similar to the central densiti es found in giant molecular clouds in the Galaxy today. It is suggeste d-that a globular cluster could reasonably form with that central dens ity with a star formation efficiency of approximate to 40 per cent and an initial mass function slope alpha approximate to 3.