R. Beck, P. Frick, R. Stepanov, D. Sokoloff
We investigate the possibilities of wavelet-based RM Synthesis for the recognition of structures of regular and turbulent magnetic fields in extended magnetized objects, like galaxies and galaxy clusters. Wavelets allow to reformulate the RM Synthesis method in a scale-dependent way and to visualize the data as a function of Faraday depth and scale. We present observational tests to recognize regular magnetic fields without and with one or two reversals along the line of sight and imprints of turbulent magnetic fields. A region with a regular magnetic field generates a broad "disk" in Faraday space ("Faraday spectrum"), with two "horns" if the distribution of cosmic-ray electrons is broader than that of the thermal electrons. Each field reversal generates one asymmetric "horn" on top of the "disk". A region with a turbulent field can be recognized by a "Faraday forest" of many components. We argue that the ratio of maximum to minimum wavelengths is an important parameter because it determines the range of scales which can be identified in Faraday space. Full recognition of magnetic field structures in spiral galaxies or galaxy clusters requires analysis of data cubes in position-position-Faraday depth ("PPF cubes"), observed over a wide and continuous wavelength range, from about 100 MHz to several GHz, providing good resolution as well as recognition of a wide range of scales in Faraday space. The planned SKA fulfils this condition and will be close to a perfect "Faraday telescope". The combination of data from the present telescopes LOFAR (low frequencies) and EVLA (high frequencies) looks promising for the recognition of magnetic structures at all scales. The addition of WSRT or GMRT data at intermediate frequencies to those from LOFAR and EVLA data fills the gap between the LOFAR and EVLA wavelength ranges.
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http://arxiv.org/abs/1204.5694
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