Nuclei of early-type dwarf galaxies: are they progenitors of UCDs?

TL;DR

This study compares the stellar populations of Virgo dwarf galaxy nuclei and UCDs, finding differences in age and metallicity overall but similarities in dense regions, supporting the idea that UCDs may originate from stripped dwarf nuclei.

Contribution

It provides new evidence that Virgo UCDs could be remnants of dwarf galaxy nuclei, based on stellar population analysis across different environments.

Findings

dE nuclei are younger and more metal-rich than UCDs overall

In high-density regions, dE nuclei and UCDs have similar ages and metallicities

Supports the hypothesis that UCDs originate from stripped dwarf galaxy nuclei

Abstract

To address the question of whether the so-called ultra compact dwarf galaxies (UCDs) are the remnant nuclei of destroyed early-type dwarf galaxies (dEs), we analyze the stellar population parameters of the nuclei of 34 Virgo dEs, as well as ten Virgo UCDs, including one that we discovered and which we report on here. Based on absorption line strength (Lick index) measurements, we find that nuclei of Virgo dEs have younger stellar population ages than UCDs, with averages of 5 Gyr and >10 Gyr, respectively. In addition to this, the metallicity also differs: dE nuclei are on average more metal-rich than UCDs. On the other hand, comparing the stellar population parameters at the same local galaxy density, with UCDs being located in the high density cluster regions, we do not find any difference in the stellar populations of dE nuclei and UCDs. In those regions, the dE nuclei are as old and as metal poor as UCDs. This evidence suggests that the Virgo UCDs may have formed through the stripping of dE nuclei.