Rotation Measure Analysis of Shocks and Sloshing Fronts in a Galaxy Cluster Merger Simulation

TL;DR

This study uses analytical and radiative transfer simulations to explore how shocks and sloshing cold fronts in galaxy clusters affect rotation measure and polarization signatures, providing insights into observed depolarization phenomena.

Contribution

It presents a detailed analysis of RM variations and depolarization effects caused by shocks and sloshing in a simulated galaxy cluster, incorporating full polarized radiative transfer calculations.

Findings

RM enhancement of ~56% behind shock fronts

RM decrement of ~23.3% behind sloshing cold fronts

Increased beam depolarization due to magnetic field fluctuations

Abstract

Recent observations of the Fornax cluster show depolarization signatures on megaparsec scales, which may be associated with shocks and/or sloshing motions during cluster merger and/or in-fall. To investigate the possible reasons behind the depolarization, we carry out analytical and full polarized radiative transfer (PRT) calculations of radio point sources behind a merging galaxy cluster simulated using the FLASH code. With uniform background light, we analyzed the rotation measure (RM) morphology near the shock front and the cluster center, where sloshing cold fronts appear. For the shock scenario, we find a local RM enhancement by $\sim56\%$ behind the shock front on megaparsec scales, arising from the compression of hot gas and magnetic field lines. Behind the sloshing cold front, the cluster center shows decrement in RM magnitude by $\sim23.3\%$, as a result of the cancellation effect of randomly-oriented magnetic fields induced by sloshing-driven turbulence. We find that beam depolarization increases behind shock fronts and across sloshing cold fronts, indicating enhanced magnetic field fluctuations across the plane of the sky in both scenarios. By fully accounting for all radiative transfer coefficients in the PRT calculations, the uniform background light becomes more depolarized near the cluster center, with the effect growing more pronounced as background intensity decreases. This suggests that synchrotron emission and Faraday rotation of the intracluster medium can significantly influence the polarization of background sources.