The Missing Link in Star Cluster Evolution

The currently most popular models for the dynamical evolution of starclusters predict that the power-law Cluster Luminosity Functions (CLFs) ofyoung star cluster systems will be transformed rapidly into the universalGaussian CLFs of old Milky Way-type "globular" cluster systems. Here, weprovide the first evidence for a turn-over in the intermediate-age,approximately 1 Gyr-old CLF in the center of the nearby starburst galaxy M82,which very closely matches the universal CLFs of old Milky Way-type globularcluster systems. This provides an important test of both cluster disruptiontheories and hierarchical galaxy formation models. It also lends strong supportto the scenario that these young cluster systems may eventually evolve into oldMilky Way-type globular cluster systems. M82's proximity, its shortest knowncluster disruption time-scale of any galaxy, and its well-defined peak ofcluster formation make it an ideal candidate to probe the evolution of its starcluster system to fainter luminosities, and thus lower masses, than has beenpossible for any galaxy before.Comment: accepted for publication in the ApJ Letters; 10 pages in AASTEX preprint format; including 2 postscript figure