THE DYNAMICAL EVOLUTION OF STELLAR SUPERCLUSTERS

Recent images taken with the Hubble Space Telescope (HST) of the inter acting disc galaxies NGC 4038/4039 (the Antennae) reveal clusters of m any dozens and possibly hundreds of young compact massive star cluster s within projected regions spanning about 100 to 500 pc, It is shown h ere that a large fraction of the individual star: clusters merge withi n a few tens to a hundred Myr. Bound stellar systems with radii of a f ew hundred parsecs, masses less than or similar to 10(9) M. and relaxa tion times of 10(11)-10(12) yr may form from these. These spheroidal d warf galaxies contain old stars from the pre-merger galaxy and much yo unger stars formed in the massive star clusters, and possibly from lat er gas accretion events. The possibility that star formation in the ou ter regions of gas-rich tidal tails may also lead to superclusters is raised. The mass-to-light ratio of these objects is small, because the y contain an insignificant amount of dark matter. After many hundred M yr such systems may resemble dwarf spheroidal satellite galaxies with large apparent mass-to-light ratios, if tidal shaping is important.