Galaxy threshing and the formation of ultra-compact dwarf galaxies

Abstract

Recent spectroscopic and morphological observational studies of galaxies around NGC 1399 in the Fornax Cluster (Drinkwater et al. 2000b) have discovered several `ultra-compact dwarf' galaxies with intrinsic sizes of $\sim$ 100 pc and absolute $B$ band magnitudes ranging from -13 to -11 mag. In order to elucidate the origin of these enigmatic objects, we perform numerical simulations on the dynamical evolution of nucleated dwarf galaxies orbiting NGC 1399 and suffering from its strong tidal gravitational field. Adopting a plausible scaling relation for dwarf galaxies, we find that the outer stellar components of a nucleated dwarf are totally removed. This is due to them being tidally stripped over the course of several passages past the central region of NGC 1399. The nucleus, however, manages to survive. We also find that the size and luminosity of the remnant are similar to those observed for ultra-compact dwarf galaxies, if the simulated precursor nucleated dwarf has a mass of $\sim$ $10^8$ $M_{\odot}$. These results suggest that ultra-compact dwarf galaxies could have previously been more luminous dwarf spheroidal or elliptical galaxies with rather compact nuclei.Comment: 9 pages 4 figures,2001, ApJL, 552, 10