Witnessing gas mixing in the metal distribution of the Hickson Compact Group HCG 31

TL;DR

This study provides direct observational evidence of gas mixing and metallicity redistribution during galaxy mergers, using detailed kinematic and metallicity data from the nearby Hickson Compact Group HCG 31.

Contribution

First direct evidence of metallicity mixing in galaxy mergers, demonstrated through detailed 2D kinematics and metallicity measurements in HCG 31.

Findings

Metallicity smoothly varies between merging nuclei

High-resolution kinematics confirm metal mixing

Merging low-mass galaxies show similar central metallicities

Abstract

We present, for the first time, direct evidence that, in a merger of disk galaxies, the preexisting central metallicities will mix as a result of gas being transported in the merger interface region, along the line that joins the two coalescing nuclei. This is shown using detailed 2D kinematics as well as metallicity measurements for the nearby ongoing merger in the center of the compact group HCG 31. We focus on the emission line gas, which is extensive in the system. The two coalescing cores display similar oxygen abundances while in between the two nuclei the metallicity changes smoothly from one nucleus to the other, indicating a mix of metals in this region, which is confirmed by the high resolution H$\alpha$ kinematics (R=45900). This nearby system is especially important because it involves the merging of two fairly low mass and clumpy galaxies (LMC-like galaxies), making it an important system for comparison with high redshift galaxies.