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Chapter 6 presents preliminary results from two-dimensional analyses of the polarization of two radio galaxies embedded in extremely different environments: 0755+37 in a very poor group and M 87 at the centre of the cool core Virgo cluster. The work of this Chapter will be published in two forecoming papers: Guidetti et al. (in preparation), Guidetti et al. (in preparation). Chapter 6.4 summarizes all the results presented and briefly lists some topics for further work. It is pointed out that this thesis has shown that the magnetized medium surrounding radio galaxies appears more complicated than was apparent from earlier work. Three distinct types of magnetic-field structure are identified: an isotropic component with large-scale fluctuations, plausibly associated with the intergalactic medium not affected by the presence of a radio source; a well-ordered field draped around the front ends of the radio lobes and a field with small-scale fluctuations in rims of compressed gas surrounding the inner lobes, perhaps associated with a mixing layer. In the Appendix new VLA polarization data for the nearby radio galaxies 0206+35, 0755+37 and M 84 are presented. This work will be published in the paper Laing, Guidetti et al. (2011, in prep). Throughout the thesis I assume a cosmology with H 0 = 71 km s −1 Mpc −1 ,Ω m = 0.3, andΩ Λ = 0.7.
Chapter 1 Physics of radio galaxies In this Chapter I will outline the essential physics required to understand the polarized emission of radio galaxies and their interactions with the local environment. Sec. 1.1 introduces radio sources in the context of active galaxies in general, and Sec. 1.2 discusses their principal emission mechanisms. The morphologies of radio galaxies, the physical parameters of their emitting regions and the implications for their interaction with the environment are described in Sec. 1.3. 1.1 Active galaxies Active galactic nuclei (AGN) are the most powerful, persistent sources of luminosity in the Universe. Their luminosities range from about 10 40 up to 10 47 ergs s −1 and their emission is spread widely across the whole electromagnetic spectrum. AGN are so called because of the current accepted model explaining their nature. They are believed to be powered by accretion onto supermassive black holes (∼ 10 7 − 10 10 M ⊙ ) located at the nuclei of so-called “active galaxies”. Indeed, the radiation emitted by such nuclei cannot be explained just by starlight or normal supernova activity and can exceed the total emission of the rest of the galaxy by many order of magnitude. Moreover, the AGN emission is often variable on time-scales ranging from years down to hours or even minutes. Causality arguments imply that an object varying in a time t must be smaller than the light-crossing time ct (where c is the speed of light in the vacuum) and therefore must be spatially small. Accretion mechanisms onto a such small object with mass≃ 10 8 M ⊙ can efficiently convert potential and kinetic energy to radiation and bulk outflow, and therefore account for high luminosities and their rapid variations. Since luminosity excesses have been observed across the entire electromagnetic waveband, there is no single observational signature of active galaxies, which can be classified in many 1
Page 1: Alma Mater Studiorum Università de
Page 5: To Hypatia from Alexandria in Egypt
Page 9 and 10: Contents Abstract i 1 Physics of ra
Page 11 and 12: 4.6.3 The outer scale of the magnet
Page 13 and 14: Abstract The existence of diffuse m
Page 15: 2. Two-dimensional Monte Carlo simu
Page 19 and 20: 1.2. Non-thermal emission mechanism
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Page 23 and 24: 1.3. Radio galaxies 7 FR II sources
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Page 27 and 28: 1.3. Radio galaxies 11 pressure, th
Page 29 and 30: Chapter 2 The X-ray environment of
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Page 37 and 38: Chapter 3 Magnetic fields in the ho
Page 39 and 40: 3.1. Introduction 23 Figure 3.1: Ex
Page 41 and 42: 3.1. Introduction 25 to the relativ
Page 43 and 44: 3.2. Faraday Rotation 27 The RM can
Page 45 and 46: 3.2. Faraday Rotation 29 Figure 3.4
Page 47 and 48: 3.3. Depolarization 31 3.3 Depolari
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4.4. Depolarization 51 Figure 4.4:
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4.4. Depolarization 53 1.25 arcsec
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4.5. Two dimensional analysis 55 sm
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4.5. Two dimensional analysis 57 Fi
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4.6. Three-dimensional analysis 59
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4.7. Summary and comparison with ot
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Chapter 5 Ordered magnetic fields a
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5.1. The Sample 75 35 49 00 ROSAT P
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5.1. The Sample 77 5.1.1 0206+35 02
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5.2. Analysis of RM and depolarizat
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5.3. Rotation measure images 81 IMA
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5.3. Rotation measure images 83 cor
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5.4. Depolarization 85 Therefore, a
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5.5. Rotation measure structure fun
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5.6. Rotation-measure bands from co
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5.7. Rotation-measure bands from a
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5.7. Rotation-measure bands from a
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5.8. Discussion 99 5.8 Discussion 5
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5.8. Discussion 101 line−of−sig
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5.8. Discussion 103 flat slopes. I
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5.9. Conclusions and outstanding qu
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5.9. Conclusions and outstanding qu
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Chapter 6 Faraday rotation in two e
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6.2. Two-dimensional analysis: rota
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6.3. Two-dimensional analysis: stru
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6.4. Preliminary conclusions 121 Ta
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6.4. Preliminary conclusions 123
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Summary and conclusions The goal of
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6.5. Summary 127 responsible for th
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6.6. General conclusions 129 radio
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6.7. Future prospects 131 and is th
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Appendix 133
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136 Data reduction and imaging of l
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144 BIBLIOGRAPHY Bîrzan, L., Raffe
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146 BIBLIOGRAPHY Ensslin, T.A. & Go
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148 BIBLIOGRAPHY Jeltema, T.E. & Pr
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150 BIBLIOGRAPHY Owen, F.N., 1989,
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152 BIBLIOGRAPHY 152
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