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40 3. Intergalactic magnetic fields (Simonetti, Cordes & Spangler 1984; Minter & Spangler 1996). It is related to the autocorrelation function C(r ⊥ ) for a sufficiently large averaging region by S (r ⊥ )=2[C(r ⊥ )−C(0)]. Laing et al. (2008) also derived the effects of convolution with the observing beam on the observed structure function. For the special case of a power-law power spectrum (their Eq. B2), they showed that the observed structure function after convolution can be heavily modified even at separations up to a few times the FWHM of the observing beam. Fig. 3.7 illustrates the effects of the convolution in two different power-law power spectra and corresponding structure function. After convolution the two power spectra are indistinguishable. This effect must be taken into account when comparing observed and predicted structure functions. However, because the suppression of power on high spatial frequencies due to the convolution, this analysis only constrains the power spectrum of the fluctuations on scales larger than the beam-width. Complementary information can be derived from numerical simulations of depolarization with fine spatial sampling (Laing et al. 2008; Guidetti et al. 2008) which constrain fluctuations of RM below the resolution limit. indeed, the use of the structure function together with the Burn law k represents a powerful technique to investigate the RM power spectrum over a wide range of spatial scales (Laing et al. 2008). In this thesis we have derived very detailed images of Faraday rotation and depolarization across radio galaxies. The next Chapters will show that all of our observations are consistent with pure foreground Faraday rotation. Where the RM structures can be reasonably approximated as isotropic, the statistics of the magnetic-field fluctuations have been quantified by deriving rotation measure structure functions, fitted using models derived from theoretical power spectra. The minimum scale of the magnetic field variations have been derived from depolarization measurements. However, I will also show that not all Faraday rotation maps are consistent with an isotropic magnetic field. This forms the most important part of my thesis and describes an unexpected phenomenon in the RM world. 40
3.7. The magnetic field power spectrum 41 Figure 3.7: (a), (c), (e): the two model RM power spectra discussed for the radio galaxy 3C 31 in Laing et al. (2008). Solid line, broken power-law power spectrum with indices q high = 11/3, q low = 2.32 and a break frequency of 0.062 arcsec −1 (their equation 8). Dashed line: power-law power spectrum with q=2.39 and a high-frequency cut-off at f max = 0.144 arcsec −1 (their equation 9). (b), (d), (f): structure functions computed for the power spectra in panels (a), (c) and (d), with the same line codes. (a) and (b) no convolution; (c) and (d) 1.5 arcsec FWHM convolving beam; (e) and (f) 5.5 arcsec FWHM convolving beam. 41
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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 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 55: 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 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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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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