Alma Mater Studiorum Universit`a degli Studi di Bologna ... - Inaf

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106 5. Ordered magnetic fields around radio galaxies both thermal density and field, and then including three- and two-dimensional stretching (“draping”) of the field lines along the direction of the radio jets (Sects. 5.6 and 5.7). Both of the mechanisms are able to generate anisotropic RM structure. 11. To reproduce the straightness of the iso-RM contours, a two-dimensional field structure is needed. In particular, a two-dimensional draped field, whose lines are geometrically described by a family of ellipses, and associated with compression, reproduces the RM bands routinely for any inclination of the sources to the line-of-sight (Sec. 5.7.3). Moreover, it might explain the high RM amplitude and low depolarization observed within the bands. 12. The invariance of the magnetic field along the axis perpendicular to the forward expansion of the lobe suggests that the physical process responsible for the draping and stretching of the magnetic field must act on scales larger than the lobe itself in this direction. It is not possible to constrain yet the scale size along the line-of-sight. 13. In order to create RM bands with multiple reversals, more complex field geometries such as two-dimensional eddies are needed (Section 5.7.4). 14. I have interpreted the observed RM’s as due to two magnetic field components: one draped around the radio lobes to produce the RM bands, the other turbulent, spread throughout the surrounding medium, unaffected by the radio source and responsible for the isotropic and random RM fluctuations (Section 5.8.3). I tested this model for 0206+35, assuming a typical variation of field strength with radius in the group atmosphere, and found that a magnetic field with central strength of B 0 = 1.8µG reproduced the RM range quite well in both lobes. 15. I have suggested two reasons for the low rate of detection of bands in published RM images: our line of sight will only intercept a draped field structure in a minority of cases and rotation by a foreground turbulent field with significant power on large scales may mask any banded RM structure. These results therefore suggest a more complex picture of the magneto-ionic environments of radio galaxies than was apparent from earlier work. I find three distinct types of magneticfield structure: an isotropic component with large-scale fluctuations, plausibly associated with the undisturbed intergalactic medium; a well-ordered field draped around the leading edges of the radio lobes and a field with small-scale fluctuations in the shells of compressed gas surrounding the inner lobes, perhaps associated with a mixing layer. In addition, I have emphasised that simple compression by the bow shock should lead to enhanced RM’s around the leading edges, but that the observed patterns depend on the pre-shock field. 106
5.9. Conclusions and outstanding questions 107 MHD simulations should be able to address the formation of anisotropic magnetic-field structures around radio lobes and to constrain the initial conditions. 107
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Alma Mater Studiorum Università de
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To Hypatia from Alexandria in Egypt
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Contents Abstract i 1 Physics of ra
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4.6.3 The outer scale of the magnet
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Abstract The existence of diffuse m
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2. Two-dimensional Monte Carlo simu
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Chapter 1 Physics of radio galaxies
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1.2. Non-thermal emission mechanism
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1.2. Non-thermal emission mechanism
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1.3. Radio galaxies 7 FR II sources
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1.3. Radio galaxies 9 (a) (b) Figur
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1.3. Radio galaxies 11 pressure, th
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Chapter 2 The X-ray environment of
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2.2. The thermal component 15 Figur
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2.3. Radio source - environment int
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2.3. Radio source - environment int
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Chapter 3 Magnetic fields in the ho
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3.1. Introduction 23 Figure 3.1: Ex
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3.1. Introduction 25 to the relativ
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3.2. Faraday Rotation 27 The RM can
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3.2. Faraday Rotation 29 Figure 3.4
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3.3. Depolarization 31 3.3 Depolari
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3.5. The magnetic field profile 33
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3.6. Tangled magnetic field 35 rad
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3.7. The magnetic field power spect
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Chapter 4 Structure of the magneto-
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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
Page 71 and 72: 4.5. Two dimensional analysis 55 sm
Page 73 and 74: 4.5. Two dimensional analysis 57 Fi
Page 75 and 76: 4.6. Three-dimensional analysis 59
Page 83 and 84: 4.7. Summary and comparison with ot
Page 89 and 90: Chapter 5 Ordered magnetic fields a
Page 91 and 92: 5.1. The Sample 75 35 49 00 ROSAT P
Page 93 and 94: 5.1. The Sample 77 5.1.1 0206+35 02
Page 95 and 96: 5.2. Analysis of RM and depolarizat
Page 97 and 98: 5.3. Rotation measure images 81 IMA
Page 99 and 100: 5.3. Rotation measure images 83 cor
Page 101 and 102: 5.4. Depolarization 85 Therefore, a
Page 103 and 104: 5.5. Rotation measure structure fun
Page 105 and 106: 5.6. Rotation-measure bands from co
Page 111 and 112: 5.7. Rotation-measure bands from a
Page 113 and 114: 5.7. Rotation-measure bands from a
Page 115 and 116: 5.8. Discussion 99 5.8 Discussion 5
Page 117 and 118: 5.8. Discussion 101 line−of−sig
Page 119 and 120: 5.8. Discussion 103 flat slopes. I
Page 121: 5.9. Conclusions and outstanding qu
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Page 127 and 128: 6.2. Two-dimensional analysis: rota
Page 135 and 136: 6.3. Two-dimensional analysis: stru
Page 137 and 138: 6.4. Preliminary conclusions 121 Ta
Page 139 and 140: 6.4. Preliminary conclusions 123
Page 141 and 142: Summary and conclusions The goal of
Page 143 and 144: 6.5. Summary 127 responsible for th
Page 145 and 146: 6.6. General conclusions 129 radio
Page 147 and 148: 6.7. Future prospects 131 and is th
Page 149: Appendix 133
Page 152 and 153: 136 Data reduction and imaging of l
Page 160 and 161: 144 BIBLIOGRAPHY Bîrzan, L., Raffe
Page 162 and 163: 146 BIBLIOGRAPHY Ensslin, T.A. & Go
Page 164 and 165: 148 BIBLIOGRAPHY Jeltema, T.E. & Pr
Page 166 and 167: 150 BIBLIOGRAPHY Owen, F.N., 1989,
Page 168 and 169: 152 BIBLIOGRAPHY 152
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