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94 5. Ordered magnetic fields around radio galaxies IMAGE: ICM.FITS IMAGE: ICM_WEAKSHOCK.FITS IMAGE: ICM_STRONGSHOCK.FITS 34 36 38 40 42 44 RAD/M/M rad m −2 40 60 80 100 120 140 160 RAD/M/M−2 rad m 100 200 300 400 500 RAD/M/M−2 rad m X X X (a) (b) (c) Figure 5.9: Panel (a): synthetic RM for a receding lobe inclined by 40 ◦ to the line-of-sight and embedded in a uniform field inclined by 60 ◦ to the line-of-sight and by and 30 ◦ to the lobe axis on the plane of the sky. Panels (b) and (c): as (a) but with a weak compression (γ max = 1.5) and a strong compression (γ max = 4) of the density and field. The crosses and the arrows indicate the position of the core and the lobe advance direction, respectively. increased. Fig. 5.9(c) illustrates the RM produced in case of the strongest possible compression, γ max = 4: the RM structure is essentially the same as in Fig. 5.9(b), with a much larger range. This very simple example shows that RM bands with amplitudes consistent with those observed can plausibly be produced even by weak shocks in the IGM, but the iso-RM contours are neither straight, nor orthogonal to the lobe axis and there are no reversals. These constraints require specific initial conditions, as illustrated in Fig. 5.10, where I show the RM for a lobe in the plane of the sky. I considered three initial field configurations: along the line-of-sight (Fig. 5.10a), in the plane of the sky and parallel to the lobe axis (Fig. 5.10b) and in the plane of the sky, but inclined by 45 ◦ to the lobe axis (Fig. 5.10c). The case closest to reproducing the observations is that displayed in Fig. 5.10(b), in which reversals and well defined and straight bands perpendicular to the jet axis are produced for both of the lobes. In Fig. 5.10(a), the structures are curved, while in Fig. 5.10(c) the bands are perpendicular to the initial field direction, and therefore inclined with respect to the lobe axis. For a source inclined by 40 ◦ to the line of sight, I found structures similar to the observed bands only with an initial field in the plane of the sky and parallel to the axis in projection (Figs 5.11a and b; note that the synthetic RM images in this example have been made for each lobe separately, neglecting superposition). I can summarize the results of the spherical pure compression model as follows. 1. An initial field with a component along the line-of-sight does not generate straight bands. 2. The bands are orthogonal to the direction of the initial field projected on the plane of the sky, so bands perpendicular to the lobe axis are only obtained with an initial field aligned with the radio jet in projection. 94
5.7. Rotation-measure bands from a draped magnetic field 95 IMAGE: BLANK.FITS IMAGE: BLANK.FITS IMAGE: BLANK.FITS 100 200 300 400 0 20 40 60 80 100 120 0 20 40 60 80 100 RAD/M/M−2 rad m RAD/M/M−2 rad m RAD/M/M−2 rad m x x x (a) (b) (c) Figure 5.10: Synthetic RM images for a lobe in the plane of the sky with an ambient field which is uniform before compression. In panels (a) and (b), the field is along the axis of the lobe in projection and inclined to the line-of-sight by (a) 45 ◦ and (b) 90 ◦ . In panel (c), the field is in the plane of the sky and misaligned by 45 ◦ with respect to the lobe axis. The crosses and the arrows represent the radio core position and the lobe advance direction, respectively. IMAGE: BLANK.FITS 0 20 40 60 80 RAD/M/M rad m −2 IMAGE: BLANK.FITS ;140 ;120 ;100 ;80 ;60 ;40 ;20 0 RAD/M/M rad m −2 x x (a) (b) Figure 5.11: Synthetic RM images of the receding (a) and approaching lobe (b) of a source inclined by 40 ◦ with respect to the line-of-sight, in the case of a uniform ambient field. The field is aligned with the radio jets in projection and inclined with respect to the line-of-sight by 90 ◦ . The crosses and the arrows represent the radio core position and the lobe advance direction, respectively. 3. The path length (determined by the precise shape of the radio lobes) has a second-order effect on the RM distribution (compare Figs. 5.9a and b). Thus, a simple compression model can generate bands with amplitudes similar to those observed but reproducing their geometry requires implausibly special initial conditions, as I discuss in the next section. 5.7 Rotation-measure bands from a draped magnetic field 5.7.1 General considerations That the pre-existing field is uniform, close to the plane of the sky and aligned with the source axis in projection is implausible for obvious reasons: 95
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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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Page 59 and 60: Chapter 4 Structure of the magneto-
Page 61 and 62: 4.1. The radio source 3C 449: gener
Page 63 and 64: 4.3. The Faraday rotation in 3C 449
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Page 67 and 68: 4.4. Depolarization 51 Figure 4.4:
Page 69 and 70: 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 107 and 108: 5.6. Rotation-measure bands from co
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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 and 122: 5.9. Conclusions and outstanding qu
Page 123 and 124: 5.9. Conclusions and outstanding qu
Page 125 and 126: Chapter 6 Faraday rotation in two e
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
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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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