Morphology of radio relics II: Properties of polarised emission

TL;DR

This paper uses 3D magneto-hydrodynamical simulations to explore how shock waves in turbulent galaxy cluster media produce polarised radio relic emission, revealing complex magnetic field structures and polarization features.

Contribution

It demonstrates that radio relics can form in tangled magnetic fields and reproduces observed polarisation features through shock compression in turbulent media.

Findings

Shock compression leads to high polarisation at the shock front.

Partial alignment of polarisation vectors with the shock normal is observed.

Simulations reproduce complex observed structures of radio relics.

Abstract

Radio relics are diffuse radio sources in galaxy clusters that are associated with merger shock waves. Detailed observations of radio relics in total intensity and in polarisation show complex structures on kiloparsec scales. The relation between the observed features and the underlying morphology of the magnetic field is not clear. Using three-dimensional magneto-hydrodynamical simulations, we study the polarised emission produced by a shock wave that propagates through a turbulent medium that resembles the intracluster medium. We model the polarised synchrotron emission on the basis of diffusive shock acceleration of cosmic-ray electrons. We find that the synchrotron emission produced in a shocked turbulent medium can reproduce some of the observed features in radio relics. Shock compression can give rise to a high polarisation fraction at the shock front and a partial alignment of the polarisation $E$-vectors with the shock normal. Our work confirms that radio relics can also be formed in an environment with a tangled magnetic field. We also discuss the effect of Faraday Rotation intrinsic to the source, and how our results depend on the angular resolution of observations.