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20 2. The X-ray environment of radio galaxies -17 00 00 2 4 6 8 -17 00 00 30 30 DECLINATION (J2000) 01 00 30 02 00 DECLINATION (J2000) 01 00 30 02 00 3 2 1 Outer 30 30 03 00 22 14 32 30 28 26 24 22 20 RIGHT ASCENSION (J2000) 03 00 22 14 32 30 28 26 24 22 20 18 RIGHT ASCENSION (J2000) Figure 2.4: (Left): Overlay of a 5 GHz VLA map (red) of 3C 444 on 0.5 - 5.0 keV Chandra data (blue) indicating the relationship between the radio and X-ray structures, including cavities coincident with the radio lobes, and a sharp elliptical surface brightness drop surrounding the source. (right): temperature map in keV with 5 GHz contours overlaid. The spectral extraction regions are numbered. The figure is taken from (Croston et al. 2010). to shock Mach numbersMof about 8 and 4 respectively (Kraft et al. 2003; Croston et al. 2007). In both the cases, the total energies stored in the cavities are several times larger than the estimated PV work. Weak shocks withM≈1.2−1.7 surrounding cavities associated with FR I and FR II sources are observed more frequently (e.g. McNamara et al. 2005; Nulsen et al. 2005a; Croston et al. 2008, 2010). Fig. 2.4 shows the case of the FR II radio galaxy 3C 444 where the surrounding intra-cluster medium is characterized by cavities and a temperature jump of a factor∼1.7, probably caused by a spheroidal shock (Croston et al. 2010). The effects of these radio-galaxy shocks on the magnetic field in the IGM are analysed in detail in Chapter 5. 20
Chapter 3 Magnetic fields in the hot phase of the intergalactic medium In this Chapter I will briefly review the state of our knowledge of intergalactic magnetic fields. Most attention is given to the results of the analysis of Faraday effect across radio galaxies, on which this thesis is based, while those from other techniques are summarized more briefly. In particular I will show that detailed radio observations of polarized radio galaxies indicate the presence of turbulent magnetic fields fluctuating over a wide range of spatial scales and provide a means of measuring their power spectra. 3.1 Introduction The existence of magnetic fields in the extragalactic universe is now well established. Our knowledge about them has greatly improved over the last few decades, mainly thanks to radio continuum observations, which have detected magnetic fields atµG levels in objects such as galaxy disks and halos and intergalactic media in both groups and clusters of galaxies. It is also possible that intergalactic voids are permeated by a widespread magnetic field. Despite their ubiquity, the role of extragalactic magnetic fields has often remained an ignored aspect of astrophysics, because of their low energy densities. µG-strength magnetic fields are now thought to be important for multiple reasons. Fields associated with the thermal IGM are not thought to be dynamically significant, since they provide typical magnetic pressures one or two orders of magnitude below thermal values. However, they are believed to strongly influence the IGM heat conductivity, inhibiting the spatial mixing of gas and propagation of cosmic rays(e.g. Balbus 2000; Bogdanović et al. 2009). Indeed, the IGM is so extremely dilute that is characterized by huge collisional mean free paths (∼20 kpc). In this condition, even for 21
Page 1: 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: 2.3. Radio source - environment int
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 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
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4.7. Summary and comparison with ot
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Chapter 5 Ordered magnetic fields a
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5.1. The Sample 75 35 49 00 ROSAT P
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5.1. The Sample 77 5.1.1 0206+35 02
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5.2. Analysis of RM and depolarizat
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5.3. Rotation measure images 81 IMA
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5.3. Rotation measure images 83 cor
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5.4. Depolarization 85 Therefore, a
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5.5. Rotation measure structure fun
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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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