An optical and X-ray study of the fossil group RX J1340.6+4018

TL;DR

This study provides an optical and X-ray analysis of the fossil group RX J1340.6+4018, revealing its similarities to galaxy clusters and offering insights into its formation and composition.

Contribution

It presents detailed observational data on RX J1340.6+4018, challenging previous claims about fossil groups lacking small mass haloes and analyzing supernova ejecta ratios.

Findings

RX J1340.6+4018 is similar to clusters in mass, luminosity, and luminosity function.

No support found for the claim that fossil groups lack small mass haloes.

Central dominance of SN Ia material suggests early formation or dry merger.

Abstract

Fossil groups are systems with one single central elliptical galaxy and an unusual lack of luminous galaxies in the inner regions. The standard explanation for the formation of these systems suggests that the lack of bright galaxies is due to galactic cannibalism. In this study we show the results of an optical and X-ray analysis of RX J1340.6+4018, the prototype fossil group. The data indicates that RX J1340.6+4018 is similar to clusters in almost every sense, dynamical mass, X-ray luminosity, M/L and luminosity function, except for the lack of L* galaxies. There are claims in the literature that fossil systems have a lack of small mass haloes, compared to predictions based on the LCDM scenario. The observational data gathered on this and other fossil groups so far offer no support to this idea. Analysis of the SN Ia/SN II ejecta ratio in the inner and outer regions shows a marginally significant central dominance of SN Ia material. This suggests that either the merger which originated the central galaxy was dry or the group has been formed at early epochs, although better data are needed to confirm this result.