Testing the tidal stripping scenario of ultra-compact dwarf galaxy formation by using internal properties

TL;DR

This study uses hydrodynamical simulations to test if ultra-compact dwarf galaxies (UCDs) form through tidal stripping, finding consistent ages, metallicities, and colours between simulated nuclei and observed UCDs, supporting the tidal stripping formation scenario.

Contribution

It provides the first detailed comparison of simulated tidally stripped nuclei properties with observed UCDs, validating the tidal stripping formation model.

Findings

Observed UCD ages > 9 Gyr match simulated nuclei.

Mass-metallicity relation is similar for UCDs and simulated nuclei.

Colours of UCDs are consistent with simulated nuclei for M > 10^7 M_sun.

Abstract

We use the hydrodynamical EAGLE simulation to test if ultra-compact dwarf galaxies (UCDs) can form by tidal stripping by predicting the ages and metallicities of tidally stripped galaxy nuclei in massive galaxy clusters, and compare these results to compiled observations of age and metallicities of observed UCDs. We further calculate the colours of our sample of simulated stripped nuclei using SSP models and compare these colours to observations of UCDs in the Virgo cluster. We find that the ages of observed UCDs are consistent with simulated stripped nuclei, with both groups of objects having a mean age > 9 Gyr. Both stripped nuclei and UCDs follow a similar mass-metallicity relationship, and the metallicities of observed UCDs are consistent with those of simulated stripped nuclei for objects with M > $10^{7}~M_{\odot}$. The colours of observed UCDs are also consistent with our simulated stripped nuclei, for objects with M > $10^{7}~M_{\odot}$, with more massive objects being redder. We find that the colours of stripped nuclei exhibit a bimodal red and blue distribution that can be explained by the dependency of colour on age and metallicity, and by the mass-colour relation. We additionally find that our low mass stripped nuclei sample is consistent with the colour of blue globular clusters. We conclude that the internal properties of simulated nuclei support the tidal stripping model of UCD formation.