Investigations of Faraday Rotation Maps of Extended Radio Sources ...

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118 CONCLUSIONS tually statistically homogeneous magnetic field can be thought to be observed. The RM maps of three radio sources (i.e. 3C75 in Abell 400, 3C465 in Abell 2634 and Hydra A in Abell 780) were reanalysed using this method. Power spectra were successfully calculated and magnetic field strengths of 1 . . . 12µG were derived for all three clusters. However, it was found that while this analysis is not suitable for the determination of differential parameters, such as the spectral slopes of power spectra, directly from the Fourier transformed map, the integrated quantities such as the magnetic field strength appears feasible. Furthermore, this analysis is not able to separate the influence of noise on the maps from the astrophysically interesting signal of intra-cluster magnetic fields. In order to reduce map making artefacts, a new algorithm – Pacman – for the calculation of Faraday rotation maps from multi-frequency polarisation data sets was developed. By means of several statistical tests, it was shown that the new algorithm Pacman is robust and that it calculates reliable RM maps that suffer less from artefacts. Any statistical analysis will profit from this improvement. Motivated by the recent success of Bayesian maximum likelihood methods in the determination of power spectra, a maximum likelihood estimator for the analysis of high quality RM maps was developed. It again assumes that the magnetic fields are statistically homogeneously distributed throughout the Faraday screen. It also allows to calculate the statistical uncertainty of any result. Furthermore, this maximum likelihood method takes the limited sampling size properly into account and thus, makes the determination of spectral slopes of power spectra possible. The maximum likelihood estimator was applied to the Pacman RM map of the north lobe of Hydra A. Taking the uncertainty in the geometry of the Faraday screen into account, the central magnetic field strength for Hydra A was determined to be 7 ± 2µG. The calculated power spectrum follows a Kolmogorov like power spectrum over at least one order of magnitude in k-space. The analysis reveals that there is a dominant scale ∼ 3 kpc on which the power is concentrated. This work will be continued in two directions, observationally and theoretically: • The developed methods will be applied to further existing and upcoming high quality RM data sets in order to gain a statistical sample of cluster field measurements. • The gained observational information will be used to understand magnetic field generating mechanisms in clusters of galaxies such as turbulent magnetic dynamos and galactic outflows.
Bibliography Allen, S. W., Taylor, G. B., Nulsen, P. E. J., et al. 2001, Mon. Not. Roy. Astron. Soc., 324, 842 Ballarati, B., Feretti, L., Ficarra, A., et al. 1981, Astron. & Astrophys., 100, 323 Beck, R. 2001, Space Science Rev., 99, 243 Beck, R., Brandenburg, A., Moss, D., Shukurov, A., & Sokoloff, D. 1996, Ann. Rev. Astron. & Astronphys., 34, 155 Bevington, P. R. & Robinson, D. K. 2003, Data reduction and error analysis for the physical sciences (Data reduction and error analysis for the physical sciences, 3rd ed., by Philip R. Bevington, and Keith D. Robinson. Boston, MA: McGraw-Hill, ISBN 0071199268, 2003.) Bicknell, G. V., Cameron, R. A., & Gingold, R. A. 1990, Astrophys. Journ., 357, 373 Bolton, J. G. & Wild, J. P. 1957, Astrophys. Journ., 125, 296 Bond, J. R., Jaffe, A. H., & Knox, L. 1998, Phys. Rev. D, 57, 2117 Bourke, T. L. & Goodman, A. A. 2004, ArXiv:astro-ph/0401281 Brentjens, M. A. & de Bruyn, A. G. 2004, in The Riddle of Cooling Flows in Galaxies and Clusters of galaxies Bridle, A. H. & Fomalont, E. B. 1976, Astron. & Astrophys., 52, 107 Burbidge, G. R. 1956, Astrophys. Journ., 124, 416 Burn, B. J. 1966, Mon. Not. Roy. Astron. Soc., 133, 67 Burns, J. O., Roettiger, K., Pinkney, J., et al. 1995, Astrophys. Journ., 446, 583 Carilli, C. L. & Taylor, G. B. 2002, Ann. Rev. Astron. & Astronphys., 40, 319 Cavaliere, A. & Fusco-Femiano, R. 1976, Astron. & Astrophys., 49, 137 Clarke, T. E. & Enßlin, T. A. 2001, in Clusters of Galaxies and the High Redshift Universe Observed in X-rays Clarke, T. E., Kronberg, P. P., & Böhringer, H. 2001, Astrophys. Journ. Let., 547, L111 119
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Investigations of Faraday Rotation
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”Vom Himmel lächelte der Herr zu
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vi CONTENTS 3.4.2 Real Space Analys
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