Testing the tidal stripping origin of ultra-compact dwarf galaxies

Abstract

Ultra-compact dwarf galaxies (UCDs) are intermediate objects between globular clusters and dwarf galaxies, with many similarities to the nuclear clusters of dwarf galaxies. Tidal stripping of nucleated galaxies is a likely origin for UCDs since tidal stripping must occur in any hierarchical galaxy formation scenario. During the tidal stripping process the main body of the galaxy is removed while the nucleus remains since the nuclear clusters are too compact to be destroyed. In this thesis I present new theoretical work addressing the possibility of UCDs having a tidal stripping origin. Through the use of N-body simulations I show that tidal stripping of nucleated galaxies in galaxy clusters under the assumption of dark matter free galaxies can account for the observed sizes and masses of UCDs. I find that incomplete stripping of the UCD progenitor galaxy, resulting in a UCD with an extended stellar envelope, may account for the observed size difference between nuclear clusters and UCDs. In a second study, I use a semi-analytic model of galaxy formation to predict the number of UCDs expected to form via tidal stripping. I find that tidal stripping cannot account for all UCDs observed in the Fornax cluster but is most important for high mass UCDs, accounting for about 50 per cent of objects with masses larger than 107M☉. Additionally, I compare the predictions for radial distributions, metallicities and implied central black hole masses from the semi-analytic models with observed UCDs in the Fornax and Virgo clusters, finding good agreement between the predictions and observations. This work suggest most UCDs are simply high-mass globular clusters, with the most massive and extended UCDs being formed by tidal stripping. Finally, I present a new method to incorporate tidal stripping of satellite galaxies into semi-analytic models of galaxy formation. Comparing with observed dwarf galaxies in the Fornax cluster, I find this method gives better agreement with the predicted numbers and radial distributions of galaxies when compared with models not taking into account tidal stripping.