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110 6. Faraday rotation in two extreme environments 1.3 arcsec the source shows a very bright core and two-sided jets embedded in an diffuse halo of low surface brightness. The jet E of the nucleus is the brighter one and the jets inclination to the line-of-sight is estimated to be about 30 ◦ (Bondi et al. 2000; Laing & Bridle in preparation) The radio source is highly polarized. 0755+35 has been observed with both the PSPC and HRI instruments on ROSAT (Worrall & Birkinshaw 1994, 2000) and with Chandra (Worrall, Birkinshaw & Hardcastle 2001). The X-ray emission has extended thermal and partially resolved non-thermal components, respectively associated with the hot medium on group and galactic scales, and with the core and jets (Canosa et al. 1999; Worrall & Birkinshaw 2000; Mulchaey et al. 2003; Wu, Feng & Xinwu 2007). However, the X-ray surface brightness profile (the sum of aβmodel and a point component) is very poorly constrained. The extent of the thermal X-ray emission is relatively small with respect to other poor groups, particularly along the EW axis of the large-scale source structure, and its luminosity is low (Worrall & Birkinshaw 2000). These arguments together with the “isolation” of 0755+37 suggest that the diffuse emission, at least on the scale of the radio emission, is mainly due to the hot atmosphere surrounding the galaxy. 6.1.2 M 87 M 87 is one of the most famous radio galaxies and resides in the gas-rich Virgo cluster, which is the nearest, bright X-ray emitting cluster. This source provides the opportunity to study the magnetic field fluctuations with excellent spatial resolution. It is a popular target of multiwavelength studies, because of its one-sided jet observed at radio (e.g. Owen 1989 (VLA); Kovalev 2007 (VLBA), optical Biretta, Sparks & Macchetto 1999) and X-ray frequencies (e.g. Forman et al. 2005, 2007; Harris et al. 2006; Churazov 2008). The morphology of the jet is similar at all these wavelengths, suggesting a common synchrotron radiation mechanism. M 87 is classified as an FR I source. On scales larger than the radio jet (∼2 kpc), it has a complex radio structure mapped out to linear scales of about 40 kpc, showing inner and outer lobes, curved “ears”, and filaments (Fig. 6.2, Owen, Eilek & Kassim 2000). The jet inclination is estimated to be about 22 ◦ (Biretta, Zhou & Owen 1995). In this work, I used VLA datasets at 5 and 8 GHz (6 cm and 3 cm respectively), which were generously provided by F. N.Owen. The VLA observations in the 6 cm band and their reduction were presented by Owen, Eilek & Keel (1990) while the 3 cm data have not been published. At these frequencies and at 0.4 arcsec resolution the source is highly polarized. The images show the main jet, pointing to NW, and two “inner lobes” extending about 4 kpc from the core (Owen, Eilek & Keel 1990). 110
6.2. Two-dimensional analysis: rotation measure and depolarization 111 Table 6.1: General optical and radio properties: Col. 1: source name; Cols. 2, 3: position; Col. 4: redshift; Col. 5: conversion from angular to spatial scale with the adopted cosmology; Col. 6: Fanaroff-Riley class; Col. 7: the largest angular size of the radio source; Col. 8: radio power at 1.4 GHz; Col. 9: angle to the line of sight of the jet axis. source RA DEC z kpc/arcsec FR class LAS θ [J2000] [J2000] [arcsec] [degree] 0755+37 07 58 28.1 +37 47 12 0.0428 0.833 I 139 30 M 87 12 30 49.4 +12 23 28 0.00436 0.089 I 489 22 Table 6.2: X-ray and radio equipartition parameters for all the sources. Col. 1: source name; Col. 2: X-ray energy band; Col. 3: average thermal temperature; Cols. 4,5,6 and 7,8,9 best-fitting core radii, central densities andβparameters for the outer and innerβmodels, respectively; Col. 10: average thermal pressure at the midpoint of the radio lobes; Cols. 11&12: minimum synchrotron pressure and corresponding magnetic field; Col.13: references for the X-ray models. source band kT r cxout n 0out β out r cxin n 0in β in P 0 P syn B Psyn ref. [keV] [keV] [kpc] [cm −3 ] [kpc] [cm −3 ] [dyne cm −2 ] [dyne cm −2 ] [µG] 0755+37 0.2-2.5 0.73 +0.32 −0.45 159 6.4×10 −4 0.9 1.7×10 −12 3.14×10 −13 4.4 1 M 87 0.7-2.7 1.68 0.04 −0.05 23.4 0.011 0.47 1.86 0.13 0.42 2.7×10−10 2.11×10 −10 55 2 References: (1) Worrall & Birkinshaw (2000); (2) Matsushita et al. (2002). Fields in the Virgo cluster centred on M 87 have been observed by several X-ray satellites. The extent of the X-ray emission is larger than 2 ◦ , which is the field of view of the ROSAT PSPC, and is centrally peaked, implying that M 87 harbours a cool core. At the ROSAT and XMM-Newton resolutions, the morphology of the X-ray emission appears regular and smooth, but deep Chandra observations (e.g. Forman et al. 2007 and references therein) have revealed a very complex structure suggesting interaction between the radio source and the hot gas on several spatial scales (Fig. 6.3). In particular, Forman et al. (2007) detected multiple cavities, some of which coincide with the inner radio lobes, rims of enhanced X-ray emission, loops, rings, and filaments. The cavities resemble the outer large-scale radio structure and have been interpreted as a system of buoyant bubbles produced in AGN outbursts. At distances of about 10-20 kpc from the core, temperature and density jumps are apparent. These correspond to weak shocks with Mach numbersM≈1.4. 6.2 Two-dimensional analysis: rotation measure and depolarization I produced RM images and related rms errors by weighted least-squares fitting to the polarization angle mapsΨ(λ) as a function ofλ 2 (Eq. 3.1) at respectively three and eight frequencies for 0755+37 and M 87 (Table 6.3) by using a version of the RM task in the AIPS package modified 111
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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
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3.6. Tangled magnetic field 35 rad
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3.7. The magnetic field power spect
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Chapter 4 Structure of the magneto-
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4.1. The radio source 3C 449: gener
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4.3. The Faraday rotation in 3C 449
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4.3. The Faraday rotation in 3C 449
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4.4. Depolarization 51 Figure 4.4:
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4.4. Depolarization 53 1.25 arcsec
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4.5. Two dimensional analysis 55 sm
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4.5. Two dimensional analysis 57 Fi
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Page 91 and 92: 5.1. The Sample 75 35 49 00 ROSAT P
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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
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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
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Page 125: Chapter 6 Faraday rotation in two e
Page 129 and 130: 6.2. Two-dimensional analysis: rota
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Page 137 and 138: 6.4. Preliminary conclusions 121 Ta
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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
Page 152 and 153: 136 Data reduction and imaging of l
Page 160 and 161: 144 BIBLIOGRAPHY Bîrzan, L., Raffe
Page 162 and 163: 146 BIBLIOGRAPHY Ensslin, T.A. & Go
Page 164 and 165: 148 BIBLIOGRAPHY Jeltema, T.E. & Pr
Page 166 and 167: 150 BIBLIOGRAPHY Owen, F.N., 1989,
Page 168 and 169: 152 BIBLIOGRAPHY 152
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