Do the stellar populations of the brightest two group galaxies depend on the magnitude gap?

TL;DR

This study examines whether the stellar populations of the brightest and second brightest galaxies in groups depend on the magnitude gap, finding no significant correlation after accounting for galaxy properties, suggesting merger history differences.

Contribution

It provides a detailed analysis of stellar populations in group galaxies using SDSS data, revealing that the magnitude gap does not significantly influence their stellar properties.

Findings

No correlation between magnitude gap and BGG stellar populations after controlling for mass.

SBGGs in large-gap groups are closer to BGGs, indicating earlier group entry.

Stellar populations of SBGGs in large-gap groups are similar to those in normal groups.

Abstract

We investigate how the stellar populations of the inner regions of the first and the second brightest group galaxies (respectively BGGs and SBGGs) vary as a function of magnitude gap, using an SDSS-based sample of 550 groups with elliptical BGGs. The sample is complete in redshift, luminosity and for $\Delta \mathcal{M}_{12}$ up to 2.5 mag, and contains 59 large-gap groups (LGGs, with $\Delta \mathcal{M}_{12} > 2.0$ mag). We determine ages, metallicities, and SFHs of BGGs and SBGGs using the STARLIGHT code with two different single stellar population models (which lead to important disagreements in SFHs), and also compute $[\alpha/{\rm Fe}]$ from spectral indices. After removing the dependence with galaxy velocity dispersion or with stellar mass, there is no correlation with magnitude gap of BGG ages, metallicities, $[\alpha/{\rm Fe}]$, and SFHs. The lack of trends of BGG SFHs with magnitude gap suggests that BGGs in LGGs have undergone more mergers than those in small-gap groups, but these mergers are either dry or occurred at very high redshift, which in either case would leave no detectable imprint in their spectra. We show that SBGGs in LGGs lie significantly closer to the BGGs (in projection) than galaxies with similar stellar masses in normal groups, which appears to be a sign of the earlier entry of the former into their groups. Nevertheless, the stellar population properties of the SBGGs in LGGs are compatible with those of the general population of galaxies with similar stellar masses residing in normal groups.