The jets in radio galaxies Martin John Hardcastle Churchill College September 1996 A dissertation submitted in candidature for the degree of Doctor of Philosophy in the University of Cambridge i `Glaucon: ª...But how did you mean the study of astronomy to be reformed, so as to serve our pur- poses?º Socrates: ªIn this way. These intricate traceries on the sky are, no doubt, the loveliest and most perfect of material things, but still part of the visibleworld, and therefore they fall far short of the true realities Ð the real relativevelocities,in theworld of purenumber and all geometrical ®gures, of the movements which carry round the bodies involved in them. These, you will agree, can be conceived by reason and thought, not by the eye.º Glaucon: ªExactly.º Socrates: ªAccordingly, we must use the embroidered heaven as a model to illustrateour study of these realities, just as one might use diagrams exquisitely drawn by some consummate artist like Daedalus. An expert in geometry, meeting with such designs, would admire their ®nished workmanship, but he wouldthink it absurd to studythem in all earnest with the expectation of ®nding in their proportionsthe exact ratio of any one number to another...º ' Ð Plato (429±347 BC), The Republic, trans. F.M. Cornford. ii Contents 1 Introduction 1 1.1 Thisthesis...................................... ... 1 1.2 Abriefhistory................................... .... 2 1.3 Synchrotronphysics........ ........... ........... ...... 4 1.4 Currentobservationalknowledgeintheradio . ............. 5 1.4.1 Jets ........................................ 6 1.4.2 Coresornuclei ................................. 6 1.4.3 Hotspots ..................................... 7 1.4.4 Largescalestructure . .... 7 1.4.5 Theradiosourcemenagerie . .... 8 1.4.6 Observationaltrends . .... 9 1.4.7 VLBI ....................................... 11 1.5 Observationalknowledgeinotherwavebands . ............ 11 1.5.1 Opticalsynchrotronradiation . ....... 11 1.5.2 Hostgalaxiesinopticalandinfra-red . ......... 12 v vi CONTENTS 1.5.3 Nuclearandextendedemissionlines. ........ 13 1.5.4 X-ray ....................................... 15 1.6 Currenttheoriesofradiosources . .......... 15 1.6.1 Thecentralengine .............................. .. 15 1.6.2 Beamsandtheproductionofradiosources . ........ 16 1.6.3 Coresandjets.................................. 16 1.6.4 Hotspotsandafter .............................. .. 17 1.6.5 Environment ................................... 18 1.6.6 Uni®edmodels .................................. 19 1.6.7 A`standardmodel'forradiosources. ........ 21 1.7 Unansweredquestions ...... ........... ........... ..... 22 1.8 Conventions..................................... ... 22 2 The observations 25 2.1 Aperturesynthesis ............................... ..... 25 2.2 TheVLA ......................................... 26 2.2.1 Observations .................................. 27 2.2.2 Datareduction ................................. 27 2.3 MERLIN ......................................... 31 2.3.1 Observations .................................. 31 2.3.2 Datareduction ................................. 31 2.4 TheRyleTelescope ................................ .... 32 3 Jets in FRIradio galaxies 35 CONTENTS vii 3.1 AsmallsampleofFRIsources . ...... 35 3.2 Observations .................................... ... 35 3.3 Sourcesindetail................................. ..... 37 3.3.1 3C66B ...................................... 38 3.3.2 3C75 ....................................... 48 3.3.3 3C130 ...................................... 53 3.3.4 3C296 ...................................... 57 3.4 Discussion...................................... ... 61 3.4.1 Velocitiesinthejets . .... 61 3.4.2 Polarization.................................. .. 64 3.4.3 Thejetsof3C66B:detailedanalysis. ........ 65 3.5 Comparisonwithothersources . ........ 70 3.6 Conclusions..................................... ... 72 4 FRIIs of intermediate luminosity 75 4.1 Introduction.................................... .... 75 4.2 Theselectionofthesample. ....... 76 4.3 TheobservationswiththeVLA. ....... 76 4.4 NewK-bandmagnitudes ..... ........... ........... .. .... 78 4.5 Sourcesindetail................................. ..... 78 4.5.1 4C12.03 ..................................... 80 4.5.2 3C20 ....................................... 80 4.5.3 3C33.1 ...................................... 83 4.5.4 3C61.1 ...................................... 86 viii CONTENTS 4.5.5 3C79 ....................................... 86 4.5.6 4C14.11 ..................................... 90 4.5.7 3C123 ...................................... 95 4.5.8 3C132 ...................................... 101 4.5.9 3C153 ...................................... 102 4.5.10 3C171 ...................................... 110 4.5.11 3C173.1 ..................................... 113 4.5.12 3C219 ...................................... 118 4.5.13 3C234 ...................................... 119 4.5.14 3C284 ...................................... 124 4.5.15 3C300 ...................................... 125 4.5.16 3C319 ...................................... 130 4.5.17 3C349 ...................................... 133 4.5.18 3C381 ...................................... 135 4.5.19 3C401 ...................................... 140 4.5.20 3C436 ...................................... 143 4.5.21 3C438 ...................................... 146 4.6 Summary ......................................... 149 4.6.1 Overallsourceproperties. ...... 149 4.6.2 Hotspots ..................................... 150 4.6.3 Jets ........................................ 153 5 Analysisof FRIIswith z 0 ¡ 3 155 5.1 Thesample ....................................... 155 CONTENTS ix 5.2 Analysisofradiomaps ...... ........... ........... ..... 156 5.2.1 Totalandlobe¯uxes ... ........... ........... .... 160 5.2.2 Cores ....................................... 160 5.2.3 Jetsandcounterjets. 162 5.2.4 Hotspots ..................................... 167 5.3 Environmentalindicators . ........ 169 6 Discussion 171 6.1 Uni®ed models at z 0 ¡ 3................................. 172 6.2 Beampowerandthestandardmodel . ....... 172 6.3 Large-scalestructure . ....... 173 6.4 Hotspots ........................................ 174 6.5 Jets ............................................ 175 6.6 Cores ........................................... 177 6.7 Beampowerandemissionlines . ...... 179 6.7.1 Introduction.................................. 179 6.7.2 Orientation-dependenceof[OIII] . ........ 179 6.7.3 Relationshipsbetween[OIII]andstraightjet . ............ 180 6.8 Sidedness ....................................... 180 6.9 Modelling....................................... 181 6.9.1 Sidedness..................................... 181 6.9.2 Coreprominence ................................ 185 6.9.3 Jetprominence ................................. 191 6.9.4 Expectedcorrelations. ..... 198 x CONTENTS 6.10 Interpretation ................................. ...... 198 6.10.1 Velocitiesanduni®edschemes . ....... 198 6.10.2 Beamef®ciency ................................ 199 6.10.3 Thelow-excitationobjects . ....... 200 7 Conclusions 219 7.1 Retrospect...................................... 219 7.2 Lessonsandmodels................................ 221 7.3 Thefuture....................................... 222 Index of radio sources 223 References 227 Chapter 1 Introduction 1.1 This thesis This thesis describes two studies of extragalactic radio sources at high resolution and sensitivity. Most of the well-known facts about radio sources come from low-resolution imaging, despite the fact that much of the interesting physics (that of the jets and hotspots) occurs on scales that are small compared to the overall source size. This thesis is an attempt to redress the balance and to extract some physical information on the energy transport in these sources from their small-scale radio structure. In this chapter I introduce extragalactic radio sources and brie¯y describe the current state of knowledge about them and the physics we might hope to extract from observations. In chapter 2 the instruments and techniques used to image sources with the required sensitivity and resolution are described. Chapter 3 is concerned with observations of a small `representative' sample of FRI sources. The features seen in the radio structures of the jets are discussed and used to estimate the physical parameters in the beams. I compare the structures seen in the jets with existing models. In chapter 4 I describe observations of a large sample of FRII sources, anddiscusssome trendsin thefea- tures observed. In chapter 5, techniques are developed for extracting quantitative information from the resulting images and from data from previous work by others, and the results are tabulated. In chapter 6 I use these results to try to constrain some physical parameters of the sources. The conclusions of the whole thesis are summed up in chapter 7. 1 2 CHAPTER 1. INTRODUCTION 1.2 A brief history In the early days of radio astronomy large numbers of bright unresolved radio sources (`radio stars') were discovered. It was soon found that many of these were associated with external galaxies, and oth- ers with star-like objects of high redshift known as quasars (Schmidt 1963). The radiation was found to be synchrotron in origin, an inference made from its spectrum and polarization (see below, section 1.3). Jennison and Das Gupta (1953) were the ®rst to note (in Cygnus A) the double structure characteristic of many of these sources;