# Ultimate Merging at z~0.1

## TL;DR

This study investigates 58 double-peaked emission line galaxies, revealing their likely merging stages, morphological features, and star formation activity, challenging simple rotation or outflow explanations.

## Contribution

It provides new insights into the merging processes and characteristics of double-peaked emission galaxies, especially the high fraction of S0 types and their morphological and spectral features.

## Key findings

- 66% of galaxies have off-centered suppressed components
- Approximately half of the sample are S0 galaxies
- Galaxies are massive, star-forming, with signs of merging or post-merger stages

## Abstract

We present a study of 58 double-peaked emission line galaxies for which one of the components is suppressed in [OIII]5008 or significantly weaker than the other one. Accordingly, the two components are classified differently in the BPT diagram. We show that the strong [OIII] component coincides with the stellar velocity and the suppressed component is off-centred in 66% of the galaxies, while in 12% of them it is the opposite. The analysis of their morphology reveals that about half of the sample is composed of S0, the rest is composed in equal part of mergers and late-type galaxies. We discuss that these characteristics exclude rotating discs and suggest different stages of merging. It is possible that the number of mergers is underestimated if the double nuclei are not resolved. Tidal features are detected in the outskirts of some S0 galaxies. This high fraction of S0 is surprising, as in addition most of the galaxies are isolated and the others in small groups. All these galaxies, hosting an AGN component, are massive, lie on the star forming sequence, and exhibit an enhanced star formation in their centre. While we cannot exclude outflows, these galaxies exhibit a spectra, which do not correspond to usual outflow observations characterised by high gas velocities, and the standard deviations of the two peaks are comparable. In parallel, these characteristics are compatible with ultimate stages of galaxy merging, where the two nuclei are too close to be detected or dynamical disturbances might be present in post-mergers like massive S0.