Enhanced mass-to-light ratios in ultracompact dwarf galaxies through tidal interaction with the centre of the host galaxy

A recent study of ultracompact dwarf galaxies (UCDs) in the Virgo cluster revealed that some of them show faint envelopes and have measured mass-to-light ratios (M/Ls) of 5 and larger, which cannot be explained by simple population-synthesis models. It is believed that this proves that some of the UCDs must possess a dark matter halo and may therefore be the stripped nuclei of dwarf ellipticals rather than merged star cluster complexes. Using an efficient N-body method, we investigate if a close passage of a UCD through the central region of the host galaxy is able to enhance the measured M/L by tidal forces leaving the satellite slightly out of virial equilibrium and thereby leading to an overestimation of its virial mass. We find this to be possible and discuss the general problem of measuring dynamical masses for objects that are probably interacting with their hosts.