Star cluster formation and evolution in the dwarf starburst galaxy NGC 1569

Abstract

We analyse multi-wavelength Hubble Space Telescope (HST) observations of a large number of star in the nearby (post-) starburst dwarf galaxy NGC 1569. Their spectral energy distributions (SEDs) cover at least the wavelength range from U to I in equivalent HST filters, in most cases supplemented by near-infrared data. Using our most up-to-date evolutionary synthesis models of the Gottingen galev code we determine ages, metallicities, extinction values and masses for each individual clus- ter robustly and independently. We confirm the youth of most of these objects. The majority were formed in a very intense starburst starting around 25 Myr ago. While there are two prominent super star clusters present in this galaxy, with masses of (5 16)×10 5 M⊙, almost all remaining are significantly less massive than an average Milky Way globular cluster, and are generally consistent with open cluster- type objects. We determine the cluster mass function from individual cluster masses derived by scaling the model SEDs of known mass to the observed cluster SEDs for each individual cluster. We find signs of a change in the cluster mass function as the burst proceeds, which we attribute to the special conditions of star cluster formation in this starburst dwarf galaxy environment.