ar X iv : a st ro - p h / 01 12 10 9 v 1 5 D ec 2 00 1 Merging Massive Star Clusters as Building Blocks of Dwarf Galaxies ?

Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal nearly unresolved 'star-like' objects with red-shifts appropriate to the Fornax-Cluster. These objects have intrinsic sizes of ≈ 100 pc and absolute B-band magnitudes in the range −14 < MB < −11.5 mag and lower limits for the central surface brightness µB ≥ 23 mag/arcsec 2 (Phillipps et al. 2001, Hilker et al. 1999), and so appear to constitute a new population of ultra-compact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar super-clusters (= clusters of star clusters; not to confuse with super stellar clusters (SSC)) by P. Kroupa (1998), which are rich aggregates of young massive star clusters (YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of super-clusters in a tidal field. The YMCs merge on a few super-cluster crossing times. Super-clusters that are initially as concentrated and massive as Knot S in the interacting Antennae galaxies (Whitmore et al. 1999) evolve to merger objects that are long-lived and show properties comparable to the newly discovered UCDs.