Contribution of stripped nuclei to the ultracompact dwarf galaxy population in the Virgo cluster

Abstract

ABSTRACT We use the hydrodynamical EAGLE simulation to predict the numbers, masses, and radial distributions of tidally stripped galaxy nuclei in massive galaxy clusters, and compare these results to observations of ultracompact dwarf galaxies (UCDs) in the Virgo cluster. We trace the merger trees of galaxies in massive galaxy clusters back in time and determine the numbers and masses of stripped nuclei from galaxies disrupted in mergers. The spatial distribution of stripped nuclei in the simulations is consistent with those of UCDs surrounding massive galaxies in the Virgo cluster. Additionally, the numbers of stripped nuclei are consistent with the numbers of M > 107 M⊙ UCDs around individual galaxies and in the Virgo cluster as a whole. The mass distributions in this mass range are also consistent. We find that the numbers of stripped nuclei surrounding individual galaxies correlate better with the stellar or halo mass of individual galaxies than the total cluster mass. We conclude that most high mass (M > 107 M⊙) UCDs are likely stripped nuclei. It is difficult to draw reliable conclusions about low mass (M < 107 M⊙) UCDs because of observational selection effects. We additionally predict that a few hundred stripped nuclei below a mass of 2 × 106 M⊙ should exist in massive galaxies that will overlap in mass with the globular cluster population. Approximately 1–3 stripped nuclei in the process of forming also exist per massive galaxy.