Seyfert's Sextet: A Slowly Dissolving Stephan's Quintet?

TL;DR

This study analyzes Seyfert's Sextet as a highly evolved galaxy group formed through sequential galaxy accretion and gas stripping, revealing slow dissolution without major mergers, contrasting with less evolved groups.

Contribution

It provides a detailed multiwavelength analysis of Seyfert's Sextet, proposing it as a more evolved analog of Stephan's Quintet with insights into galaxy evolution and group dissolution processes.

Findings

Seyfert's Sextet formed by sequential galaxy accretion over 2-3 Gyr.

Most member galaxies show early-type morphology due to gas stripping.

Evidence of past accretion events and slow dissolution without major mergers.

Abstract

We present a multiwavelength study of the highly evolved compact galaxy group known as Seyfert's Sextet (HCG79: SS). We interpret SS as a 2-3 Gyr more evolved analog of Stephan's Quintet (HCG92: SQ). We postulate that SS formed by sequential acquisition of 4-5 primarily late-type field galaxies. Four of the five galaxies show an early-type morphology which is likely the result of secular evolution driven by gas stripping. Stellar stripping has produced a massive/luminous halo and embedded galaxies that are overluminous for their size. These are interpreted as remnant bulges of the accreted spirals. H79d could be interpreted as the most recent intruder being the only galaxy with an intact ISM and uncertain evidence for tidal perturbation. In addition to stripping activity we find evidence for past accretion events. H79b (NGC6027) shows a strong counter-rotating emission line component interpreted as an accreted dwarf spiral. H79a shows evidence for an infalling component of gas representing feedback or possible cross fueling by H79d. The biggest challenge to this scenario involves the low gas fraction in the group. If SS formed from normal field spirals then much of the gas is missing. Finally, despite its advanced stage of evolution, we find no evidence for major mergers and infer that SS (and SQ) are telling us that such groups coalesce via slow dissolution.