A Multiple Dry Merger at z=0.18: Witnessing The Assembly of a Massive Elliptical Galaxy

TL;DR

This paper reports the discovery and analysis of a rare low-redshift galaxy group undergoing a multiple dry merger, providing insights into the formation of massive elliptical galaxies.

Contribution

It presents the first detailed observational evidence of a possible quintuple dry merger at low redshift, combining SDSS data and follow-up spectroscopy.

Findings

The system is a low-redshift, isolated galaxy group with massive, quiescent galaxies.

The galaxies are in close proximity with small projected separations and specific mass ratios.

Simulations suggest the system will likely merge into a single massive elliptical galaxy.

Abstract

Mergers of gas-poor galaxies, so-called dry mergers, may play a fundamental role in the assembly of the most massive galaxies, and therefore, in galaxy formation theories. Using the SDSS, we have serendipitously discovered a rare system in the observational and theoretical context, possibly a quintuple dry merger at low redshift. As a follow-up, we have obtained NOT long-slit spectra of the group, in order to measure the individual redshifts and gain insight into its merger fate. Our results show an isolated, low-redshift galaxy group consisting of massive, quiescent, early-type galaxies, composed of two clumps (possibly themselves in the process of merging), which we estimate will hypothetically merge in roughly less than a Gyr. With the possible exception of the high line-of-sight velocity dispersion, the overall properties of the system may be comparable to a compact Shakhbazyan group. However, when the small projected separations and relative mass ratios of the galaxies are taken into account in cosmological simulations, we find that this system is rather unique. We hypothesize that this group is a dry merger, whose fate will result in the assembly of an isolated, massive elliptical galaxy at low redshift.