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

TL;DR

This study uses hydrodynamical simulations to show that most high-mass ultra-compact dwarf galaxies in the Virgo Cluster are likely stripped galaxy nuclei, matching observed distributions and numbers.

Contribution

It provides the first detailed comparison of simulated stripped nuclei with observed UCDs, supporting their origin as tidally stripped galaxy nuclei.

Findings

Simulated spatial distribution matches observed UCDs in Virgo.

Numbers of high-mass UCDs align with predictions for stripped nuclei.

Most high-mass UCDs are likely remnants of galaxy nuclei.

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 ultra-compact 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 > $10^{7}~M_{\odot}$ 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 correlates better with the stellar or halo mass of individual galaxies than the total cluster mass. We conclude that most high mass (M > $10^{7}~M_{\odot}$ UCDs are likely stripped nuclei. It is difficult to draw reliable conclusions about low mass (M < $10^{7}~M_{\odot}$ UCDs because of observational selection effects. We additionally predict that a few hundred stripped nuclei below a mass of $2~\times~10^{6}~M_{\odot}$ 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.