A major galaxy cluster merger caught by eROSITA: weak lensing mass distribution and kinematic description

TL;DR

This paper uses weak lensing data from eROSITA to analyze a triple galaxy cluster merger, confirming the major merger status, estimating the merger timeline, and clarifying the gravitational binding of the clusters.

Contribution

It provides the first weak lensing mass distribution analysis of this specific triple cluster merger and clarifies the dynamical state and gravitational binding of the involved clusters.

Findings

Confirmed a major merger with a mass ratio of approximately 1.7.

Estimated the merger occurred about 0.58 Gyr ago.

Determined the companion cluster is not gravitationally bound.

Abstract

We present the weak lensing mass distribution of a triple merging cluster candidate at $z_{\rm photo}\sim 0.36$ belonging to a supercluster recently discovered during the eROSITA Performance Verification phase. Our analysis solved a previous tension in the merger classification by confirming that the cluster pair eFEDS J093513.3+004746 and eFEDS J093510.7+004910 is undergoing a major merger with a mass ratio $1.7_{-0.7}^{+0.5}$. According to our two-body kinematic description, the encounter happened $0.58_{-0.20}^{+0.15}$ Gyr ago, in a scenario that supports the observed radio relic position at the cluster outskirts. However, the same analysis showed that the companion cluster, eFEDS J093501.1+005418, is not gravitationally bound to the interacting system and therefore it is not part of the supercluster. We also checked the impact of adopting a scaling relation to determine the halo concentration $c_{200}$. At the observed merger stage, where the clusters have travelled $\sim$55 per cent of the path to reach the apoapsis, the choice of the $c_{200}$ (whether from a scaling relation or a free parameter in the mass model) does not change significantly either the cluster masses or the kinematic description.