The dynamo origin of magnetic fields in galaxy clusters

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Abstract
We consider the generation of magnetic fields by turbulent motions of intracluster gas in rich galaxy clusters. A qualitative discussion of the properties of intracluster MHD turbulence, its spectrum, characteristic scales and velocities, and estimation of hydrodynamic and magnetic Reynolds numbers is presented. Turbulence arises in the wakes of galaxies which move transonically through the gas. Magnetic field is generated at scales below the energy-range scale of turbulence. The magnetic fields are concentrated within thin intense ropes which occupy a small fraction of the total volume. The field strength within the ropes is about 10 µG, as determined by equipartition with kinetic energy of turbulence, while the rms field strength within a turbulent cell is as low as 2 µG. The correlation function of the chaotic magnetic field has a number of characteristic scales ranging from 20 kpc (the turbulence correlation scale) to 2 × 10−3 kpc (the skin-layer thickness). The results are in agreement with observations of magnetic fields in the radiohaloes of galaxy clusters, in particular with recent observations of Cygnus A.

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