The formation of ultra-compact dwarf galaxies and their black holes in a cosmological simulation

Ultra-compact dwarf galaxies (UCDs) are intermediate objects between star clusters and galaxies. One theory of UCD formation is that they are the stripped nuclei of dwarf galaxies that were tidally disrupted by mergers with other galaxies. Recent observations have detected supermassive black holes in a few massive UCDs, supporting this formation hypothesis. However previous numerical simulations of the process have not had the resolution to model the presence of UCDs or their black holes. We have used the state-of-the-art EAGLE simulation to model the formation of UCDs. We have done this by tracking the most bound particles of galaxies that are stripped in the simulation, which we then identify as UCDs. The EAGLE simulation allows us to determine the size of the black hole that was in the progenitor galaxy and now resides in the surviving UCD. We compared the radial distributions and masses of the simulated stripped nuclei to observed UCD populations and found them to be consistent, suggesting that UCDs likely are stripped nuclei. Our next step will be to determine the black hole masses of the simulated stripped nuclei and compare them with the black holes observed in UCDs. This will allow us to make a more accurate comparison of the black hole populations predicted by the EAGLE simulation with observed black hole populations.