E+S galaxy pairs: are they the precursors of fossil groups?

TL;DR

This study investigates galaxy pairs with giant ellipticals and spirals to understand their evolution into fossil groups, revealing that X-ray properties do not always correlate with galaxy population and that some pairs may be transitional stages.

Contribution

It provides new insights into the environmental and evolutionary differences of galaxy pairs with varying X-ray emissions, suggesting a possible pathway to fossil group formation.

Findings

X-ray luminous pairs are more dynamically evolved than similar X-ray luminous poor groups.

X-ray faint pairs have luminosity functions similar to X-ray bright groups, indicating a transitional evolutionary phase.

X-ray faint groups' properties are consistent with evolution into fossil groups.

Abstract

Galaxy pairs may represent a way station in the evolutionary path from poor groups to giant isolated ellipticals (or fossil groups). To test this evolutionary scenario, we investigated the environment of 4 galaxy pairs composed of a giant elliptical galaxy and its spiral companion. The pairs are very similar from the optical and dynamical point of view, but have very different X-ray properties. The faint galaxy population around the pairs was observed with VIMOS on the VLT. These observations show that the presence of extended diffuse X-ray emission from an IGM is not necessarily connected to the presence of a numerous faint galaxy population. The study of luminosity functions (LFs) indicate that our X-ray luminous pairs are more dynamically evolved than a sample of poor groups with comparable X-ray luminosities from the literature. However, our X-ray faint pairs resemble the LF of those X-ray bright groups and may represent a phase in the dynamical evolution of these groups, where the recent or ongoing interaction, in which the pair E is involved, has destroyed or at least decreased the luminosity of the IGM. The X-ray faint groups' LF is also consitent with their evolution into a fossil group.