Young Massive Clusters - Formation Efficiencies and (Initial) Mass Functions

Globular Clusters are often assumed to be good tracers of major star formation episodes in their host galaxies. While observations over the past 2 decades have confirmed the presence of voting objects with globular cluster-like properties in many galaxies, it is still riot well understood exactly how the formation efficiency of bound star clusters relative to field stars and their mass spectrum depend on external factors. The cluster initial mass function typically appears to be consistent with a power-law with a slope similar to - 2, but most attempts to constrain any tipper limit oil the CIMF have been limited by size-of-sample effects. However, evidence is starting to accumulate for possible truncation of the cluster mass function. It is tentatively suggested that the upper mass limit may currently be at similar to 10(5) M (D in the Milky Way disk, while there are indications that it is similar to 5 x 10(5) M-circle dot in M51 and about 2 x 10(6) M-circle dot in the Antennae. Some extreme starbursts (e.g. Arp 220, NGC 7252) are (or were) able to form clusters as massive as 10(7) M-circle dot. The overall formation efficiency of star clusters (relative to field stars) in the Galactic bulge may riot have been much different from that in tire disk today, but was probably significantly higher for metal-poor GCs in halos.