The Missing Link in Star Cluster Evolution
نویسنده
چکیده
The currently most popular models for the dynamical evolution of star clusters predict that the power-law Cluster Luminosity Functions (CLFs) of young star cluster systems will be transformed rapidly into the universal Gaussian CLFs of old Milky Way-type “globular” cluster systems. Here, we provide 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 globular cluster systems. This provides an important test of both cluster disruption theories and hierarchical galaxy formation models. It also lends strong support to the scenario that these young cluster systems may eventually evolve into old Milky Way-type globular cluster systems. M82’s proximity, its shortest known cluster disruption time-scale of any galaxy, and its well-defined peak of cluster formation make it an ideal candidate to probe the evolution of its star cluster system to fainter luminosities, and thus lower masses, than has been possible for any galaxy before. Subject headings: galaxies: evolution — galaxies: individual (M82) — galaxies: starburst — galaxies: star clusters 1. The Cluster Luminosity Function For old globular cluster systems, with ages in excess of ∼ 10 yr, the shape of the cluster luminosity function (CLF) is well-established: it is roughly Gaussian, with an apparently universal peak luminosity, M V ≃ −7.4 mag, and a Gaussian FWHM ∼ 3 mag (e.g., Whitmore et al. 1995, Harris 1996, 2001, Ashman & Zepf 1998, Harris et al. 1998). On
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