Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

TL;DR

This study analyzes galaxy mergers in the GAMA survey, revealing merger rates, properties, and environmental factors, showing that mergers contribute minimally to red sequence buildup and that paired galaxies are generally redder and more spheroid-dominated.

Contribution

It provides the first detailed measurement of merger fractions, rates, and properties as a function of luminosity and morphology in the local universe using GAMA data.

Findings

Merger fraction is about 1.5% across luminosities.

Volume merger rate is approximately 0.00035 per Mpc^3 per Gyr.

Dry mergers are rare and decrease with lower luminosity.

Abstract

We derive the close pair fractions and volume merger rates as a function of luminosity and morphology for galaxies in the GAMA survey with -23 < M(r) < -17 at 0.01 < z < 0.22. The merger fraction is about 0.015 at all luminosities (assuming 1/2 of pairs merge) and the volume merger rate is about 0.00035 per cubic Mpc per Gyr. Dry mergers (between red or spheroidal galaxies) are uncommon and decrease with decreasing luminosity. Fainter mergers are wet, between blue or disky galaxies. Damp mergers (one of each type) follow the average of dry and wet mergers. In the brighter luminosity bin (-23 < M(r) < -20) the merger rate evolution is flat, irrespective of colour or morphology. The makeup of the merging population does not change since z = 0.2. Major mergers and dry mergers appear comparatively unimportant in the buildup of the red sequence over the past 2 Gyr. We compare the colour, morphology, environmental density and degree of activity of galaxies in pairs to those of more isolated objects in the same volume. Galaxies in close pairs tend to be both redder and slightly more spheroid-dominated. This may be due to "harassment" in multiple previous passes prior to the current interaction. Galaxy pairs do not appear to prefer significantly denser environments. There is no evidence of an enhancement in the AGN fraction in pairs, compared to other galaxies in the same volume.