Magnetic fields and Faraday rotation in clusters of galaxies

By M. Murgia, F. Govoni, L. Feretti, G. Giovannini, D. Dallacasa, R. Fanti, G. B. Taylor, Klaus Dolag. 2004

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We present a numerical approach to investigate the relationship between magnetic fields and Faraday rotation effects in clusters of galaxies. We can infer the structure and strength of intra-cluster magnetic fields by comparing our simulations with the observed polarization properties of extended cluster radio sources such as radio galaxies and halos. We find the observations require a magnetic field which fluctuates over a wide range of spatial scales (at least one order of magnitude). If several polarized radio sources are located at different projected positions in a galaxy cluster, as is the case for A119, detailed Faraday rotation images allow us to constrain both the magnetic field strength and the slope of the power spectrum. Our results show that the standard analytic expressions applied in the literature overestimate the cluster magnetic field strengths by a factor of ∼2. We investigate the possible effects of our models on beam depolarization of radio sources whose radiation traverses the magnetized intracluster medium. Finally, we point out that radio halos may provide important information about the spatial power spectrum of the magnetic field fluctuations on large scales. In particular, different values of the index of the power spectrum produce very different total intensity and polarization brightness distributions.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/8a2837ed38829d5046a1273c899f8f7b7c7ea319

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Citations in the corpus

Evolving turbulence and magnetic fields in galaxy clusters (2005, background): “Govoni et al. (2005) report detection of polarized emission from filamentary structures in the cluster A2255, of a size 180 × 540 kpc2 (see also Murgia et al. 2004), but the orientation of the polarization plane mostly disagrees with the above suggestions, unless the amount of foreground Faraday…”
Massive and refined - II. The statistical properties of turbulent motions in massive galaxy clusters with high spatial resolution (2010, background): “These studies show that the magnetic ﬁeld in the ICM is tan-gled on a broad range of spatial scales (e.g. Murgia et al. 2004; Vogt & Ensslin 2005; Bonafede et al. 2010; Govoni et al. 2010; Vacca et al. 2010) suggesting the presence of super–Alfv´enic motions in the medium.”
Revised equipartition and minimum energy formula for magnetic field strength estimates from radio synchrotron observations (2005, background): “Finally, Newmanet al. (2002) and Murgia et al. (2004) pointed out that field estimates based on Faraday rotation measures are likely to be too high by a factor of a few if there is a spectrum of turbulence scales.”
Cluster magnetic fields from galactic outflows (2008, methodology): “…dependence of the magnetic field can be inferred from clusters where rotation measures of several radio galaxies are available (Dolag et al. 2001b; Murgia et al. 2004; Govoni 2006), there still exits a large degeneracy between the parameters describing the magnetic field in clusters (Bonafede et…”
A Bayesian view on Faraday rotation maps - Seeing the magnetic power spectra in galaxy clusters (2005, methodology): “Recently, Murgia et al. (2004) proposed a numerical method to determine the magnetic power spectrum in clusters.”
The intracluster magnetic field power spectrum in Abell 665 (2007, methodology): “As pointed out in Murgia et al. (2004), there are a number of degeneracies between these parameters.”
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR (2009, background): “Also studies of Faraday Rotation allow a complementary approach and suggest that the IGM magnetic field is turbulent on a broad range of scales (Murgia et al.2004; Govoni et al.2006; Ensslin & Vogt (2006).”
The Coma cluster magnetic field from Faraday rotation measures (2009, methodology): “We analyzed new Very Large Array (VLA) polarimetric observations of seven sources in the Coma cluster field, and used the FARADAY code developed by Murgia et al. (2004) to derive the magnetic field model that best represents our data through numerical simulations.”