Galaxy threshing and the formation of ultracompact dwarf galaxies

Recent spectroscopic and morphological observational studies of galaxies ar ound NGC 1399 in the Fornax Cluster have discovered several "ultracompact d warf" galaxies with intrinsic sizes of similar to 100 pc and absolute B-ban d magnitudes ranging from -13 to -11 mag. In order to elucidate the origin of these enigmatic objects, we perform numerical simulations on the dynamic al evolution of nucleated dwarf galaxies orbiting NGC 1399 and suffering fr om its strong tidal gravitational field. Adopting a plausible scaling relat ion for dwarf galaxies, we find that the outer stellar components of a nucl eated 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. T he nucleus, however, manages to survive. We also find that the size and lum inosity of the remnant are similar to those observed for ultracompact dwarf galaxies, if the simulated precursor nucleated dwarf has a mass of similar to 10(8) M.. These results suggest that ultracompact dwarf galaxies could have previously been more luminous dwarf spheroidal or elliptical galaxies with rather compact nuclei.