Diffuse radio emission from clusters in the MareNostrum Universe simulation

TL;DR

This study uses cosmological simulations to identify shock fronts and estimate diffuse radio emission in galaxy clusters, reproducing observed radio relic properties and linking them to cluster merger dynamics.

Contribution

Introduces a novel shock identification method in SPH simulations and estimates radio emission, matching observed relic features and their dependence on cluster temperature.

Findings

Radio relic morphology similar to observations in several clusters.

Maximum diffuse radio emission correlates with cluster X-ray temperature.

Moderate shock acceleration efficiency and magnetic fields reproduce relic statistics.

Abstract

Large-scale diffuse radio emission is observed in some clusters of galaxies. There is ample of evidence that the emission has its origin in synchrotron losses of relativistic electrons, accelerated in the course of clusters mergers. In a cosmological simulation we locate the structure formation shocks and estimate their radio emission. We proceed as follows: Introducing a novel approach to identify strong shock fronts in an SPH simulation, we determine the Mach number as well as the downstream density and temperature in the MareNostrum Universe simulation which has 2x1024^3 particles in a 500 Mpc/h box and was carried out with non-radiative physics. Then, we estimate the radio emission using the formalism derived in Hoeft & Brueggen (2007) and produce artificial radio maps of massive clusters. Several of our clusters show radio objects with similar morphology to large-scale radio relics found in the sky, whereas about half of the clusters show only very little radio emission. In agreement with observational findings, the maximum diffuse radio emission of our clusters depends strongly on their X-ray temperature. We find that the so-called accretion shocks cause only very little radio emission. We conclude that a moderate efficiency of shock acceleration, namely xi_e <= 0.005, and moderate magnetic fields in the region of the relics, namely 0.07 to 0.8 muGauss are sufficient to reproduce the number density and luminosity of radio relics.