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52 4. The magneto-ionic medium around 3C 449 IMAGE: K;BURN_4P_2000.FITS IMAGE: K;BURN_5.5.FITS ;400 ;200 0 200 400 600 ;400 ;200 0 200 400 600 800 1000 39 24 00 39 27 00 39 23 00 39 24 00 DECLINATION (J2000) 39 22 00 39 21 00 DECLINATION (J2000) 39 21 00 (c) 39 20 00 39 18 00 39 19 00 (a) 22 31 24 22 31 21 22 31 18 RIGHT ASCENSION (J2000) (b) 22 31 30 22 31 24 22 31 18 22 31 12 RIGHT ASCENSION (J2000) (d) Figure 4.5: (a): image of the Burn law k in rad 2 m −4 computed from a fit to the relation p(λ) = p(0) exp(−kλ 4 ) for seven frequencies between 1.365 and 8.385 GHz. (b): as (a), but the angular resolution is 5.5 arcsec FWHM, and the k image has been computed computed from the fit to the six frequencies between 1.365 and 4.985 GHz. (c) and (d): profiles for k as functions of the projected distance from the radio source center (boxes as in Fig. 4.2). The horizontal and vertical bars represent the bin widths and the error on the mean, respectively. Positive distances are in the direction of the north jet, and the vertical dashed lines show the position of the nucleus. with p>4σ p at each frequency are included in the fits. I estimate that any bias is negligible compared with the fitting error. I also derived profiles of k with the same sets of boxes as for the σ RM profiles in Fig. 4.2. The 1.25 arcsec resolution k map is shown in Fig. 4.5(a), together with the profile of the k values (Fig. 4.5c). The fit to aλ 4 law is very good everywhere: examples of fits at selected pixels in the jets and lobes are shown in in Fig. 4.6. The symmetry observed in theσ RM profiles is also seen in the 1.25 arcsec k image (Fig. 4.5): the mean values of k are≃50 rad 2 m −4 for both lobes, 107 and 82 rad 2 m −4 for the northern and southern jet, respectively. The region with the highest depolarization is in the northern jet, very close to the core and along the west side. The integrated value of k at this resolution is≃56 rad 2 m −4 , corresponding to a mean depolarization DP 20cm 3cm ≃ 0.87. The image and profile of k at 5.5-arcsec resolution are shown in Fig. 4.5(b) and (d). The fit 52
4.4. Depolarization 53 1.25 arcsec 5.5 arcsec Figure 4.6: Plots of degree of polarization, p (log scale) againstλ 4 for representative points at 1.25-arcsec and 5.5-arcsec resolution. Burn law fits (Eq. 3.5) are also plotted. The values of k are quoted in the individual panels. to aλ 4 law is in general good and examples are shown in in Figs. 4.6. As mentioned earlier, the maximum scale of structure imaged accurately in total intensity at 5 GHz is∼300 arcsec (100 kpc) and there are likely to be significant systematic errors in the degree of polarization on larger scales. I therefore show the profile only for the inner±50 kpc. Over this range, the k profiles are quite symmetrical, as at higher resolution. Note also that the small regions of very high k at the edge of the northern and southern spurs in the map shown in Fig. 4.5 are likely to be spurious. The mean values of k are≃184 rad 2 m −4 and 178 rad 2 m −4 for the northern and southern lobes, respectively; and≃238 and 174 rad 2 m −4 in the northern and in the southern spurs. The integrated value of k is≃194 rad 2 m −4 , corresponding to a depolarization DP 20cm 6cm ≃ 0.64. To summarize, depolarization between 20 cm and 3 cm is observed. Since I measure lower values of k at 1.25 arcsec than 5.5 arcsec, there is less depolarization at high resolution, as expected for beam depolarization. The highest depolarization is observed in a region of the northern jet, close to the radio core and associated with a steep RM gradient. Depolarization is significantly higher close to the nucleus, which is consistent with the higher path length through the group gas observed in X-rays. Aside from this global variation, I found no evidence for a detailed correlation of depolarization with source structure. Depolarization and RM data are therefore both consistent with a foreground Faraday screen. In Sec. 4.5.2 I show that the residual depolarization at 1.25- arcsec resolution can be produced by RM fluctuations on scales smaller than the beam-width, but higher-resolution observations are needed to establish this conclusively. 53
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Alma Mater Studiorum Università de
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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
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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
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: 4.4. Depolarization 51 Figure 4.4:
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
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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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