Disturbed Fossil Group Galaxy NGC 1132

TL;DR

This study analyzes Chandra X-ray data of NGC 1132, revealing a disturbed hot gas halo contrary to expectations for fossil groups, suggesting recent merger activity and prompting a reevaluation of fossil system characteristics.

Contribution

The paper provides the first detailed X-ray analysis showing that NGC 1132's hot halo is disturbed, indicating recent merger activity in a system previously thought to be relaxed.

Findings

Hot gas morphology is disturbed and asymmetrical.

Evidence of a cold front and possible bow shock.

Likely recent minor merger activity.

Abstract

We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e. a system expected to be old and relaxed long after the giant elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas morphology is disturbed and asymmetrical, with a cold front following a possible bow shock. We discuss possible origins of the disturbed hot halo, including sloshing by a nearby object, merger, ram pressure by external hotter gas and nuclear outburst. We consider that the first two mechanisms are likely explanations for the disturbed hot halo, with a slight preference for a minor merger with a low impact parameter because of the match with simulations and previous optical observations. In this case, NGC 1132 may be a rare example of unusual late mergers seen in recent simulations. Regardless of the origin of the disturbed hot halo, the paradigm of the fossil system needs to be reconsidered.