Multi-colour Imaging of Ultra-compact Objects in the Fornax Cluster

Abstract

Ultra-compact dwarf galaxies (UCDs) are a new type of galaxy we have discovered in the central region of the Fornax and Virgo clusters. Unresolved in ground-based imaging, UCDs have spectra typical of old stellar systems. Ninety-two have been found in Fornax, making them the most numerous galaxy type in the cluster. Here we present multicolour (u'g'r'i'z') imaging of the central region of the Fornax Cluster using the CTIO 4m Mosaic Telescope. The colour-magnitude relation for bright UCDs is qualitatively consistent with UCDs being the stripped nuclei of dE,Ns. However at faint magnitudes, GCs and UCDs cannot be distinguished by colour alone. High resolution spectroscopy to measure their internal velocity dispersions and metallicities, is needed to distinguish between GCs and UCDs.