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IMAGE: XMM_AS_1.3_OGEOM.FITS CNTRS: 1.3_5.5_I_2000_XMM.FITS 0.5 1 1.5 2 2.5 44 4. The magneto-ionic medium around 3C 449 39 30 00 100 kpc DECLINATION (J2000) 39 25 00 39 20 00 N Spur N Jet S Lobe S Jet N Lobe S Spur 39 15 00 22 32 00 22 31 30 22 31 00 RIGHT ASCENSION (J2000) 22 30 30 Figure 4.1: Radio contours of 3C 449 at 1.365 GHz superposed on the XMM-Newton X-ray image (courtesy of J. Croston, Croston et al. 2003). The radio contours start at 3σ I and increase by factors of 2. The restoring beam is 5.5 arcsec FWHM. The main regions of 3C 449 discussed in the text are labelled. 2231.2+3732 (Zwicky & Kowal 1968) The source is relatively nearby (z=0.017085, RC3.9, de Vaucouleurs et al. 1991) and quite extended, both in angular (30 arcmin) and linear size, so it is an ideal target for an analysis of the Faraday rotation distribution: detailed images can be constructed that can serve as the basis of an accurate study of magnetic field power spectra. The source 3C 449 was one of the first radio galaxies studied in detail with the VLA (Perley, Willis & Scott 1979). High- and low-resolution radio data already exist and the source has been mapped at many frequencies. The radio emission of 3C 449 (Fig. 4.1) is elongated in the N–S direction and is characterized by long, two-sided jets with a striking mirror symmetry close to the nucleus. The jets terminate in well-defined inner lobes, which fade into well polarized tails (spurs), of which the southern one is more collimated. The spurs in turn expand to form diffuse outer lobes. The brightness ratio of the radio jets is very nearly 1, implying that they are close to the plane of the sky if they are intrinsically symmetrical and have relativistic flow velocities similar to those 44
4.1. The radio source 3C 449: general properties 45 derived for other FR I jets (Perley, Willis & Scott 1979; Feretti et al. 1999a; Laing & Bridle 2002a). Therefore the jets are assumed to lie exactly in the plane of the sky, which simplifies the geometry of the Faraday-rotating medium. Hot gas associated with the galaxy was detected on both the group and the galactic scales by X-ray imaging (Hardcastle, Worrall & Birkinshaw, 1998; Croston et al. 2003). These observations revealed deficits in the X-ray surface brightness at the positions of the outer radio lobes, suggesting interactions with the surrounding material. Figure 4.1 shows radio contours at 1.365 GHz overlaid on the X-ray emission as observed by the XMM-Newton satellite (Croston et al. 2003). The X-ray radial surface brightness profile of 3C 449 derived from these data can be fitted with the sum of a point-source convolved with the instrumental response and aβmodel (Cavaliere & Fusco-Femiano 1976): n e (r)=n 0 (1+r 2 /rc) 2 − 3 2 β , (4.1) where r, r c and n 0 are the distance from the group X-ray center, the group core radius, and the central electron density, respectively. Croston et al. (2008) found a best fitting model with β=0.42±0.05, r c = 57.1 arcsec and n 0 = 3.7×10 −3 cm −3 . In these calculations, I assumed that the group gas density is described by the model of Croston et al. (2008). The X-ray depressions noted by Croston et al. (2003) are at distances larger than those at which it is possible to detect linear polarization, and there is no direct evidence of smaller cavities close to the nucleus. I therefore neglect any departures from the spherically-symmetrical density model, noting that this approximation may become increasingly inaccurate where the source widens (i.e. in the inner lobes and spurs). The source 3C 449 resembles 3C 31 in environment and in radio morphology: both sources are associated with the central members of groups of galaxies, and their redshifts are very similar. The nearest neighbours are at a projected distances of about 30 kpc in both cases. Both radio sources have large angular extents, bending jets and long, narrow tails with low surface brightnesses and steep spectra, although 3C 31 appears much more distorted on large scales. There is one significant difference: the inner jets of 3C 31 are thought to be inclined by≈50 ◦ to the line-of-sight (Laing & Bridle 2002a), whereas those in 3C 449 are likely to be close to the plane of the sky (Feretti et al. 1999a). It is therefore expected that the magnetized foreground medium will be very similar in the two sources, but that the geometry will be significantly different, leading to a much more symmetrical distribution of Faraday rotation in 3C 449 compared with that observed in 3C 31 by Laing et al. (2008). 45
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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
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 59: Chapter 4 Structure of the magneto-
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
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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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