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6 Faraday rotation in two extreme environments 109 6.1 The sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.1.1 B2 0755+37 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.1.2 M 87 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 6.2 Two-dimensional analysis: rotation measure and depolarization . . . . . . . . . . 111 6.2.1 0755+37: images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.2.2 M 87: images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 6.3 Two-dimensional analysis: structure functions . . . . . . . . . . . . . . . . . . . 118 6.4 Preliminary conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Summary and conclusions 125 6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 6.5.1 The tailed source 3C 449 . . . . . . . . . . . . . . . . . . . . . . . . . . 125 6.5.2 The lobed radio galaxies 0206+35, 3C 270, M 84 and 3C 353 . . . . . . . 126 6.5.3 The radio galaxies 0755+37 and M 87 . . . . . . . . . . . . . . . . . . . 127 6.6 General conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 6.7 Future prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Appendix 133 Data reduction and imaging of lobed radio galaxies 135 .1 Observations and VLA data reduction . . . . . . . . . . . . . . . . . . . . . . . 135 .2 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 .2.1 0206+35 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 .2.2 0755+37 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 .2.3 M 84 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Bibliography 143 Acknowledgments 153
Abstract The existence of diffuse magnetic fields ofµG strength in the hot intergalactic medium is now well established. Our knowledge about them has greatly improved over the last few decades, mainly thanks to radio continuum observations, which have detected synchrotron emission from cluster diffuse sources (halos and relics) and Faraday rotation of polarized emission from embedded and/or background radio galaxies. Such fields are not thought to be dynamically significant, since they provide typical magnetic pressures one or two orders of magnitude below thermal values. However, they are believed to strongly influence the heat conductivity in the intergalactic medium and to inhibit the spatial mixing of gas and propagation of cosmic rays. Therefore, in order to improve our knowledge of the physical processes in the gaseous environment of galaxies, accurate measurements of quantities such as magnetic field strength, spatial variation, topology and power spectrum are crucial. While most work until recently has been devoted to rich clusters of galaxies, little attention has been given to sparser environments, such as groups of galaxies, although similar physical processes are likely to be at work. The purpose of this thesis is to investigate the strength and structure of the magnetized medium surrounding radio galaxies via observations of the Faraday effect. This study is based on an analysis of the polarization properties of radio galaxies selected to have a range of morphologies (elongated tails, or lobes with small axial ratios) and to be located in a variety of environments (from rich cluster core to small group). The targets include famous objects like M 84 and M 87. A key aspect of this work is the combination of accurate radio imaging with high-quality X-ray data for the gas surrounding the sources. Although the focus of this thesis is primarily observational, I developed analytical models and performed two- and three-dimensional numerical simulations of magnetic fields. The steps of the thesis are: (a) to analyze new and archival observations of Faraday rotation measure (RM) across radio galaxies and (b) to interpret these and existing RM images using sophisticated two and three-dimensional Monte Carlo simulations. i
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: 4.6.3 The outer scale of the magnet
Page 15 and 16: 2. Two-dimensional Monte Carlo simu
Page 17 and 18: Chapter 1 Physics of radio galaxies
Page 19 and 20: 1.2. Non-thermal emission mechanism
Page 21 and 22: 1.2. Non-thermal emission mechanism
Page 23 and 24: 1.3. Radio galaxies 7 FR II sources
Page 25 and 26: 1.3. Radio galaxies 9 (a) (b) Figur
Page 27 and 28: 1.3. Radio galaxies 11 pressure, th
Page 29 and 30: Chapter 2 The X-ray environment of
Page 31 and 32: 2.2. The thermal component 15 Figur
Page 33 and 34: 2.3. Radio source - environment int
Page 35 and 36: 2.3. Radio source - environment int
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
Page 49 and 50: 3.5. The magnetic field profile 33
Page 51 and 52: 3.6. Tangled magnetic field 35 rad
Page 53 and 54: 3.7. The magnetic field power spect
Page 59 and 60: Chapter 4 Structure of the magneto-
Page 61 and 62: 4.1. The radio source 3C 449: gener
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4.3. The Faraday rotation in 3C 449
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4.3. The Faraday rotation in 3C 449
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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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