Volume 529, May 2011
|Number of page(s)||13|
|Section||Cosmology (including clusters of galaxies)|
|Published online||21 March 2011|
Magnetic power spectra from Faraday rotation maps
REALMAF and its use on Hydra A
Max Planck Institute for Astrophysics, Karl-Schwartzschildstr.1, 85741 Garching, Germany
Received: 19 December 2009
Accepted: 29 January 2011
We develop a novel maximum-a-posteriori method to measure magnetic power spectra from Faraday rotation data and implement it in the REALMAF code. A sophisticated model for the magnetic autocorrelation in real space permits us to alleviate previously required simplifying assumptions in the processing. We also introduce a way to treat the divergence relation of the magnetic field with a multiplicative factor in Fourier space, with which we can model the magnetic autocorrelation as a spherically symmetric function. Applied to the dataset of Hydra A north, we find a power law power spectrum on spatial scales between 0.3 kpc and 8 kpc, with no visible turnover at large scales within this range and a spectral index consistent with a Kolmogorov-like power law regime. The magnetic field strength profile seems to follow the electron density profile with an index α = 1. A variation of α from 0.5 to 1.5 would lead to a spectral index between 1.55 and 2.05. The extrapolated magnetic field strength in the cluster centre highly depends on the assumed projection angle of the jet. For an angle of 45° we derive extrapolated 36 μG in the centre and directly probed 16 μG at 50 kpc radius.
Key words: magnetic fields / galaxies: clusters: intracluster medium / radio continuum: general / polarization / turbulence / plasmas
© ESO, 2011
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