The Formation of Globular Clusters and of The Stars Within Them

Abstract

We propose that proto-globular cluster clouds form in a collapsing protogalactic cloud as a consequence of thermal instability. The clouds are photoionized and heated by nearby massive stars. Most are not self-gravitating, but are confined by the residual hot gas in the protogalactic cloud. Their masses evolve as they undergo cohesive collisions with each other and erosion due to interaction with the residual halo gas. Collisions may also trigger thermal instability and fragmentation within protocluster clouds. The resulting cloudlets are pressure confined, and fall toward the center of the protocluster cloud due to inverse buoyancy. Their mass distribution is also regulated by coagulation and erosion. While most cloudlets have substellar masses, the largest become self-gravitating, and collapse to form protostellar cores without further fragmentation. The initial stellar mass function is established as these cores capture additional residual cloudlets. Energy dissipation from the mergers ensures that the cluster will remain bound in the limit of low star formation efficiency. Dissipation also promotes the formation and retention of the most massive stars in the cluster center.