Cold fronts in galaxy clusters

TL;DR

This study investigates the occurrence and origins of cold fronts in galaxy clusters using XMM-Newton data, revealing their association with merger events and entropy gradients, and estimating merger rates.

Contribution

It provides a systematic analysis of cold fronts in a large cluster sample, linking their presence to merger activity and internal cluster properties for the first time.

Findings

Majority of clusters host at least one cold front.

Cold fronts are linked to merger events and entropy gradients.

Estimated merger rate is at least one per halo per Gyr.

Abstract

Cold fronts have been observed in a large number of galaxy clusters. Understanding their nature and origin is of primary importance for the investigation of the internal dynamics of clusters. To gain insight on the nature of these features, we carry out a statistical investigation of their occurrence in a sample of galaxy clusters observed with XMM-Newton and we correlate their presence with different cluster properties. We have selected a sample of 45 clusters starting from the B55 flux limited sample by Edge et al. (1990) and performed a systematic search of cold fronts. We find that a large fraction of clusters host at least one cold front. Cold fronts are easily detected in all systems that are manifestly undergoing a merger event in the plane of the sky while the presence of such features in the remaining clusters is related to the presence of a steep entropy gradient, in agreement with theoretical expectations. Assuming that cold fronts in cool core clusters are triggered by minor merger events, we estimate a minimum of 1/3 merging events per halo per Gyr.