The Origin of the Gaussian Initial Mass Function of Globular Cluster Systems

Abstract

Evidence favouring a Gaussian initial mass function (IMF) for systems of old globular clusters (GC) has accumulated over recent years. We show that a bell-shaped mass function may be the imprint of expulsion from the protocluster of the leftover star forming gas due to supernova activity. Owing to the corresponding weakening of its gravitational potential, the protocluster retains a fraction only of its newly formed stars. The mass fraction of bound stars extends from zero to unity depending on the star formation efficiency (SFE) achieved by the protoglobular cloud. We investigate how such wide variations affect the mapping of the protoglobular cloud mass function to the GC IMF. An initial power-law cloud mass function generates cluster IMFs which are bell-shaped, with a turnover whose location is mostly driven by the lower limit of the cloud mass range.