Polarisation of Radio Relics in Galaxy Clusters

TL;DR

This study uses high-resolution cosmological simulations to analyze the polarisation properties of radio relics in galaxy clusters, comparing mock observations with real data to understand magnetic field structures.

Contribution

The paper introduces a new analysis method of cosmological simulations to study radio relic polarisation and compares simulated results with observations across multiple frequencies and telescopes.

Findings

Simulations reproduce observed polarisation degrees.

Faraday rotation complicates magnetic field structure interpretation below 1.4 GHz.

Some small-scale features match real relics, but large-scale structures like 'Sausage' and 'Toothbrush' are not fully reproduced.

Abstract

Radio emission in the form of giant radio relics is observed at the periphery of galaxy clusters. This non-thermal emission is an important tracer for cosmic-ray electrons and intracluster magnetic fields. One striking observational feature of these objects is their high degree of polarisation which provides information on the magnetic fields at the relics' positions. In this contribution, we test if state-of-the-art high resolution cosmological simulations are able to reproduce the polarisation features of radio relics. Therefore, we present a new analysis of high-resolution cosmological simulations to study the polarisation properties of radio relics in detail. In order to compare our results with current and future radio observations, we create mock radio observations of the diffuse polarised emission from a massive galaxy clusters using six different projections, for different observing frequencies and for different telescopes. Our simulations suggest that, due to the effect of Faraday rotation, it is extremely difficult to relate the morphology of the polarised emission for observing frequencies below $1.4 \ \mathrm{GHz}$ to the real magnetic field structure in relics. We can reproduce the observed degree of polarisation and also several small-scale structures observed in real radio relics, but further work would be needed to reproduce some large-scale spectacular features as observed in real radio relics, such as the "Sausage" and the "Toothbrush" relics.