Metallicity of high stellar mass galaxies with signs of merger events

TL;DR

This study investigates the relationship between metallicity, morphology, and merger activity in high stellar mass galaxies, revealing that lower metallicity galaxies are more often disturbed and have younger stellar populations, indicating recent mergers.

Contribution

It provides a systematic analysis linking metallicity, morphological disturbance, and stellar population age in high mass galaxies, highlighting the prevalence of recent mergers in low metallicity systems.

Findings

Higher fraction of disturbed galaxies at lower metallicity.

Disturbed low metallicity galaxies have younger stellar populations.

Disturbed low metallicity galaxies are bluer, indicating recent star formation.

Abstract

We focus on an analysis of galaxies of high stellar mass and low metallicity. We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high resolution imaging and both spectroscopic and photometric information available in the SDSS database. For each galaxy in our sample, we conducted a systematic morphological analysis by visual inspection of MGC images using their luminosity contours. The galaxies are classified as either disturbed or undisturbed objects. We divide the sample into three metallicity regions, within wich we compare the properties of disturbed and undisturbed objects. We find that the fraction of galaxies that are strongly disturbed, indicative of being merger remnants, is higher when lower metallicity objects are considered. The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed galaxies (for high, medium, and low metallicity, respectively). Moreover, the ratio of the disturbed to undisturbed relative distributions of the population age indicator, Dn(4000), in the low metallicity bin, indicates that the disturbed objects have substantially younger stellar populations than their undisturbed counterparts. In addition, we find that an analysis of colour distributions provides similar results, showing that low metallicity galaxies with a disturbed morphology are bluer than those that are undisturbed. The bluer colours and younger populations of the low metallicity, morphologically disturbed objects suggest that they have experienced a recent merger with an associated enhanced star formation rate. [abridged]