SUPERNOVAE, GLOBULAR-CLUSTERS, AND GALAXY MERGERS

A number of lines of evidence show that collisions, and subsequent mergers, of gas-rich disk galaxies can trigger bursts of star and cluster formation. Observations of NGC 4038/4039 (the Antennae) appear to show that the young clusters formed during this merger have an exponential (open cluster) luminosity function, rather than a Gaussian (globular cluster) luminosity function. This result militates against the suggestion that the high specific globular cluster frequency in elliptical galaxies is due to globular cluster formation during mergers. The observation that [alpha/Fe] is larger in ellipticals than it is in spirals shows that elliptical galaxies must have formed on a shorter timescale than spirals. This would appear to rule out evolutionary models in which the majority of ellipticals formed from mergers between mostly stellar disk systems. Scenarios in which the protogalactic halo was locally homogeneous, but globally heterogeneous and clumpy, may account for the puzzling observation that Galactic globular dusters exhibit both age differences of a few gigayears and high [alpha/Fe] values.