A multiple dry merger at z=0.18: witnessing the assembly of a massive elliptical galaxy

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 Sloan Digital Sky Survey, 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 Nordic Optical Telescope 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.