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86 5. Ordered magnetic fields around radio galaxies 3C 270 also shows areas of very strong depolarization (k∼550 rad 2 m −4 , corresponding to DP=0.35) close to the core and surrounding the inner and northern parts of both the radio lobes. As for M 84, the areas of high k are coincident with ridges in the X-ray emission which form the boundaries of the cavity surrounding the lobes (Fig. 5.6(b)). The inner parts of this X- ray structure are described in more detail by Worrall et al. (2010), whose recent high-resolution Chandra image clearly reveals “wedges” of low brightness surrounding the radio jets. As in M 84, the most likely explanation is that a shell of denser gas immediately surrounding the radio lobes is magnetized, with significant fluctuations of field strength and density on scales smaller than the 5-arcsec beam, uncorrelated with the RM bands. The k profile of 3C 270 (Fig. 5.5(f)) is very symmetrical, suggesting that the magnetic-field and density distributions are also symmetrical and consistent with an orientation close to the plane of the sky. The largest values of k are observed in the centre, coincident with the features noted earlier and with the bulk of the X-ray emission (the high k values in the two outermost bins have low signal-to-noise and are not significant). In the Burn law k image of 3C 353, there is evidence for a straight and knotty region of high depolarization≈20 kpc long and extending westwards from the core. This region does not appear to be related either to the jets or to any other radio feature. As in M 84 and 3C 270, the RM appears quite smooth over the area showing high depolarization, again suggesting that there are two scales of structure, one much smaller than the beam, but producing zero mean RM and the other very well resolved. In 3C 353, there is as yet no evidence for hot or cool ionized gas associated with the enhanced depolarization (contamination from the very bright nuclear X-ray emission affects an area of 1 arcmin radius around the core; Iwasawa et al. 2000, Goodger et al. 2008). The k profile of 3C 353 (Fig. 5.5(h)) shows a marked asymmetry, with much higher values in the East. This is in the same sense as the difference of RM fluctuation amplitudes (Fig. 5.5(g)) and is also consistent with the eastern lobe being embedded in higher-density gas. The relatively high values of k within 20 kpc of the nucleus in the Western lobe are due primarily to the discrete region identified earlier. 5.5 Rotation measure structure functions I calculated RM structure function (Eq. 3.13) for discrete regions of the sources where the RM fluctuations appear to be isotropic and random and for which we expect the spatial variations of foreground thermal gas density, rms magnetic field strength and path length to be reasonably small. These are: the inner 26 arcsec of the receding (Eastern) lobe of 0206+35, the inner 100 arcsec of 3C 270 and the inner 40 arcsec of the western lobe of 3C 353. The selected areas of 0206+35 and 3C 270 are both within the core radii of the larger-scale beta models that describe the group- 86
5.5. Rotation measure structure functions 87 Table 5.5: Power spectrum parameters for the individual sub-regions. Col. 1: source name; Col. 2: angular resolution; Col. 3: slope q: Col. 4: amplitude C 0 ; Col. 5: minimum scale; Col. 6: amplitude of the large scale isotropic component; Col. 7: observed mean k; Col. 8: predicted mean k. The power spectrum has not been computed for M 84 (see Section 5.5). source FWHM q log C 0 Λ min A iso k obs k syn [arcsec] [kpc] [rad m −2 ] [rad 2 m −4 ] [rad 2 m −4 ] 0206+35 1.2 2.1 0.77 2 10 37 40 3C 270 1.65 2.7 0.90 0.1 5 30 26 5.0 2.7 0.90 0.1 5 71 64 3C 353 1.3 3.1 0.99 0.1 10 38 33 M 84 1.65
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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
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
Page 63 and 64: 4.3. The Faraday rotation in 3C 449
Page 65 and 66: 4.3. The Faraday rotation in 3C 449
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: 5.4. Depolarization 85 Therefore, a
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 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
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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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