Double-nucleus elliptical MCG-01-12-005 in an X-ray emitting cluster of galaxies

TL;DR

This paper reports the discovery of a double-nucleus elliptical galaxy within an X-ray emitting cluster, providing evidence of a galaxy merger in progress, supported by photometric and spectroscopic analysis.

Contribution

It presents a detailed observational case of a merging elliptical galaxy with two nuclei, confirmed by consistent redshifts and spectral features, adding to understanding of galaxy formation processes.

Findings

Two nuclei have similar colors and spectra, indicating a merger.

Redshifts of both nuclei match, confirming they are part of the same galaxy.

The galaxy is located in an X-ray emitting cluster, supporting the merger scenario.

Abstract

The scenario of galaxy formation is believed to follow a structure that builds up from the bottom, with large galaxies being formed by several merging episodes of smaller ones. In this scenario a number of galaxies can be expected to be seen in the merging phase, with their external regions already mixed, while their nuclei, with stronger self-gravitation, are still recognizable as such. During a photometric monitoring of AGNs in the field of a long-exposure INTEGRAL pointing, we serendipitously found an elliptical galaxy in the center of the X-ray cluster (EXO 0422-086) with two nuclei. We performed surface photometry on our images and those of the SDSS archive and obtained slit spectra of both nuclei. Aperture photometry of the two stellar-like nuclei showed very similar colors in the SDSS image and in our Johnson BVRI images, which is typical of an elliptical galaxy nucleus. The spectra of the nuclei showed the typical absorption lines of an elliptical galaxy without appreciable emission lines. The redshifts derived from each nucleus were equal and fully consistent with the literature value (0.0397). We can therefore exclude the possibility that one of the nuclei is a foreground star or a background AGN and consider this elliptical galaxy as a bona fide example of a galaxy merger.