Journal Article

Magnetic field amplification by shocks in galaxy clusters: application to radio relics

Luigi Iapichino and Marcus Brüggen

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 3, pages 2781-2788
Published in print July 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI:
Magnetic field amplification by shocks in galaxy clusters: application to radio relics

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Merger shocks induce turbulence in the intracluster medium (ICM), and, under some circumstances, accelerate electrons to relativistic velocities to form so-called radio relics. Relics are mostly found at the periphery of galaxy clusters and appear to have magnetic fields at the μ G level. Here we investigate the possible origins of these magnetic fields. Turbulence produced by the shock itself cannot explain the magnitude of these fields. However, we argue that if the turbulent pressure support in the ICM upstream of the merger shock is of the order of 10–30 per cent of the total pressure on scales of a few times 100 kpc, then vorticity generated by compressive and baroclinic effects across the shock discontinuity can lead to a sufficient amplification of the magnetic field. Compressional amplification can explain the large polarization of the radio emission more easily than dynamo turbulent amplification. Finally, clumping of the ICM is shown to have a negligible effect on magnetic field amplification.

Keywords: magnetic fields; shock waves; turbulence; methods: analytical; galaxies: clusters: general

Journal Article.  6876 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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