Some Constraints on the Formation of Globular Clusters

We explore the constraints on globular cluster formation provided by theobserved conditions in starbursts where globulars are currently forming, and bythe observed properties of young and old globular clusters. We note that thepressure in the ISM of starbursts and mergers implies that molecular clouds inthese environments have radii similar to those of globular clusters. Suchmolecular clouds are therefore viable precursors to globular clusters if thestar formation efficiency in the clouds is high. A high star formationefficiency may be a consequence of the high density and associated high bindingenergy and short dynamical timescale of molecular clouds in such environments.We also note that the apparent lack of a mass-radius relationship in young andold globular cluster systems places important constraints on globular clusterformation models. This is because molecular clouds are observed to follow avirial scaling relation between mass and radius. We suggest that a variablestar formation efficiency may weaken or eliminate the mass-radius relation ofmolecular clouds as they fragment to form globular clusters. We attribute theabsence of young globular clusters in the disks of ordinary galaxies such asthe Milky Way to the relatively low ambient pressures in such systems.Comment: 12 pages. Accepted for publication in the Astronomical Journal, Oct 1st issu