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116 6. Faraday rotation in two extreme environments 0755+37 Figure 6.6: Profiles of Burn law k for 0755+37 parallel to the jet direction, plotted against distance from the nucleus. The angular resolutions are 4.0 (left) and 1.3 arcsec FWHM (right). Apart from the cone-like structure in the E lobe no correlation of depolarization with source morphology is apparent. Together with the absence of significant deviations fromλ 2 rotation, this is again consistent with a Faraday rotating medium mostly external to the source. 6.2.2 M 87: images I made the RM image of M 87 at a resolution of 0.4 arcsec. TheRM task did not solve correctly for the nπ ambiguities in position angle at some locations. In order to remove these ambiguities, the RM map was produced using the following steps: 1. Fit to the four frequencies in the 3 cm band using the Greg Taylor version of theRM program inAIPS. This produced a noisy, but smooth RM image. 2. RunMWFLT inAIPS on this RM image, to apply a median-weight filter with a 15-pixel (1.5 arcsec) smoothing kernel. 3. Correct all of the polarization angle maps (in the 6 and 3 cm bands) using the filtered RM image. 4. Run a modified version ofRM task which minimises the absolute differences between the polarization angle maps at adjacent frequencies (i.e. assumes that there are no nπ ambiguities). 5. Add the result back to the filtered RM image. The resulting RM map essentially confirms the results of the 4-frequency, C-band fit made by Owen, Eilek & Keel (1990), but is significant improved both in noise level and overall reliability. 116
6.2. Two-dimensional analysis: rotation measure and depolarization 117 IMAGE: M87.RMRAL_BLANK.FITS DECLINATION (J2000) 12 23 45 12 23 30 12 23 15 12 23 00 ;2000 0 2000 4000 6000 RAD/M/M 1 kpc 12 22 45 12 30 52 12 30 51 12 30 50 12 30 49 12 30 48 RIGHT ASCENSION (J2000) 12 30 47 Figure 6.7: Rotation measure of M 87 computed from fits to the position angle –λ 2 rotation at eight frequencies as described in the text. The angular resolution is 0.4 arcsec FWHM. The new map, shown in Fig. 6.7, has an average fitting errorσ RMfit = 15 rad m −2 . The RM distribution has a mean of roughly 650 rad m −2 withσ RM ≈900 rad m −2 . The main features of the RM image are as follows. • The RM values are large and almost always positive, requiring a magnetic field pointing towards us across most of the source. They range from≈−2000 up to≈6000 rad m −2 . This compares with the much larger range of−1000-8000 rad m −2 found by Owen, Eilek & Keel (1990). The most extreme positive values found by are Owen, Eilek & Keel (1990) not consistent with the X-band position angles. • The highest RM values (≈3500-6000 rad m −2 ) are seen only in a restricted patch in the E lobe. • The jet appears as a uniform RM structure characterized by low values (≈100 rad m −2 ), as already pointed out by Owen, Eilek & Keel (1990). • The RM distribution is asymmetrical: positive and smoothly varying in the W lobe, patchier and associate with field reversals in the E lobe. As in 0755+37, the low RM seen across the jet is surprising. Similar explanations may hold for the two sources. 117
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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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4.6. Three-dimensional analysis 59
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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
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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
Page 119 and 120: 5.8. Discussion 103 flat slopes. I
Page 121 and 122: 5.9. Conclusions and outstanding qu
Page 123 and 124: 5.9. Conclusions and outstanding qu
Page 125 and 126: Chapter 6 Faraday rotation in two e
Page 127 and 128: 6.2. Two-dimensional analysis: rota
Page 129 and 130: 6.2. Two-dimensional analysis: rota
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Page 135 and 136: 6.3. Two-dimensional analysis: stru
Page 137 and 138: 6.4. Preliminary conclusions 121 Ta
Page 139 and 140: 6.4. Preliminary conclusions 123
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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