Nuclei of early-type dwarf galaxies: insights from stellar populations

TL;DR

This study analyzes the stellar populations of 26 early-type dwarf galaxies in the Virgo cluster, revealing that nuclei are generally younger and more metal-rich than their host galaxies, with diverse radial gradients.

Contribution

It provides the first detailed comparison of stellar populations between nuclei and main bodies in a sizable sample of Virgo dwarf galaxies, highlighting age and metallicity differences.

Findings

Nuclei are typically younger than their host galaxies by about 3.5 Gyr.

Most nuclei are more metal-rich than their surrounding galaxy.

Radial gradients show increasing age and decreasing metallicity with radius.

Abstract

(Abridged) We present a comprehensive analysis of the spatially resolved stellar population properties of 26 early-type dwarf (dE) galaxies in the Virgo cluster. Using Lick/IDS absorption line indices we derive simple stellar population(SSP)-equivalent age, metallicity and [$\alpha$/Fe] abundance ratio. In particular, we focus on the comparison of the stellar populations between the central nucleus and the surrounding galactic main body. The stellar populations of the nuclei are, for most dEs, significantly younger than those of the respective galactic main bodies, with an average difference of 3.5 Gyr. We find only five dEs with significantly older nuclei than their galactic main bodies. Furthermore, we observe most dE nuclei to be more metal rich compared to their host galaxies. These age and metallicity behaviours are shown by almost all dEs brighter than M$_{\it r}$ = -17 mag. We also examine the presence of radial gradients in the SSP parameters for a subset of 13 dEs (up to 1.2 kpc or 15 arcsec radius). We notice two different types of gradients, namely smooth profiles that include the nucleus, and profiles where a break occurs between the nucleus and the rest of the galaxy. Nevertheless, an overall trend of increasing age and decreasing metallicity with radius exists, consistent with earlier studies.