Star Formation Efficiencies and Star Cluster Formation

Starbursts produce large numbers of Young Star Clusters (YSCs). Multi-color photometry in combination with a dedicated SED analysis tool allows to derive ages, metallicities, EB−V, and masses including 1σ uncertainties for individual clusters and, hence, mass functions for YSC systems. The mass function, known to be Gaussian for old Globular Cluster (GC) systems, is still controversial for YSC systems. GC formation is expected in massive gas-rich spiral – spiral mergers because of their high global star formation efficiencies and observed in ≥ 1 Gyr old merger remnants. Yet it has not been possible to identify young GCs among YSC populations. We suggest a compactness parameters involving masses and half-light radii of YSCs to investigate if young GCs are formed in starbursts and if the ratio of young GCs to more loosely bound star clusters depends on galaxy type, mass, burst strength, etc. 1. Star Formation Efficiencies & Star Cluster Formation Both burst strengths b defined by the relative increase of the stellar mass in the course of starbursts, b := ∆Sburst Stotal , and Star Formation Efficiencies (SFEs) defined as the total stellar mass formed out of an available mass of gas, SFE :=