Magnetic turbulence in cool cores of galaxy clusters

Abstract

Abstract. We argue that the recently reported Kolmogorov-like magnetic turbulence spectrum in the cool core of the Hydra A galaxy cluster can be understood by kinetic energy injection by active galaxies that drives a turbulent non-helical magnetic dynamo into its saturated state. Although dramatic differences exist between small-scale dynamo scenarios, their saturated state is expected to be similar, as we show for three scenarios: the ¤ux rope dynamo, the ¤uctuation dynamo, and the explosive dynamo. Based on those scenarios, we develop an analytical model of the hydrodynamic and magnetic turbulence in cool cores. The model implies magnetic £eld strengths that £t well with Faraday rotation measurements and minimum energy estimates for the sample of cool core clusters having such data available. Predictions for magnetic £elds in clusters for which the appropriate observational information is still missing, and for yet unobserved quantities like the hydrodynamical turbulence velocity and characteristic length-scale are provided. The underlying dynamo models suggest magnetic intermittency and possibly a largescale hydrodynamic viscosity. We conclude that the success of the model to explain the £eld strength in cool core clusters indicates that in general cluster magnetic £elds directly re¤ect hydrodynamical turbulence, also in clusters without cool cores.

Propagation of Ultra–High‐Energy Cosmic Rays above 1019eV in a Structured Extragalactic Magnetic Field and Galactic Magnetic Field

“…Physically, one expects l cut Tl c , but we set l cut ¼ 1 8 l c in order to save the CPU time. We use n H ¼ À11/3, corresponding to the Kolmogorov spectrum, since the Faraday rotation map reveals that the clusters' magnetic fields are turbulent with the Kolmogorov spectrum over at least 1 order of magnitude of the wavenumber ( Vogt & Ensslin 2004). …”

The growth of baryonic structure in the presence of cosmological magnetic pressure

“…For these values, the highest normalization models challenge the latest observational constraints for the magnetic energy density in clusters obtained from Faraday rotation measures (Vogt & Enlin 2006). Our models were chosen to span the full range of possible magnetic field strengths, with the strongest fields larger than observed (and so producing consequences larger than expected in the observed Universe).…”

A STUDY OF BROADBAND FARADAY ROTATION AND POLARIZATION BEHAVIOR OVER 1.3–10 GHz IN 36 DISCRETE RADIO SOURCES

“…Typically, RM variations across radio sources embedded in ICMs are observed to be ∼ a few hundred rad m −2 in the emitting frame (e.g. Murgia et al 2004, Govoni et al 2010, Bonafede et al 2010), but can exceed thousands of rad m −2 for the inner-most regions of cooling core clusters (Perley & Taylor 1991, Vogt & Enßlin 2006. However, lmc s11, lmc c02 & lmc c04 are completely spatially unresolved over 1.3-10 GHz, while lmc c03 is dominated by an unresolved component in the 6/3 cm bands (see Fig.…”