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Environments of Powerful Radio Galaxies Through the Cosmic Ages

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Environments of Powerful Radio Galaxies Through the Cosmic Ages UNIVERSITY OF SOUTHAMPTON Environments of powerful radio galaxies through the cosmic ages Julie-Ann Goodlet arXiv:astro-ph/0602374v1 16 Feb 2006 Submitted for the degree of Doctor of Philosophy DEPARTMENT OF PHYSICS AND ASTRONOMY FACULTY OF SCIENCE July 7, 2018 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF SCIENCE DEPARTMENT OF PHYSICS AND ASTRONOMY Doctor of Philosophy Environments of powerful radio galaxies through the cosmic ages by Julie-Ann Goodlet I define 3 samples of extragalactic radio sources of type FRII, containing 26 objects in total. The control sample consists of 6C and 7C sources with radio– luminosities of around 1027 W Hz−1 at 151 MHz and redshifts of z 1. The other samples contain 3CRR sources with either comparable redshifts but∼ radio lumi- nosities about a decade larger or with comparable radio–luminosities but redshifts around z 0.4. These samples are used to investigate the possible evolution of depolarisation∼ and rotation measure properties with redshift and radio luminosity independently. All sources show evidence for an external Faraday screen. Depo- larisation and variations in the rotation measure of a source increase with redshift, only the depolarisation measure shows any trend with radio-luminosity. There are no strong trends with spectral index. I use the Kaiser et al. (1997) model with 3 flux measurements to estimate the density of the source environment, source age and jet power. Depolarisation and variations in the rotation measure were found to be insensitive to changes in the density of the source environment. This indicates that depolarisation and variations in the rotation measure are not density indicators but map how the disorder in the magnetic field changes with redshift. The model is then used on a larger set of FRII sources taken from the complete 3CRR, 6CE and 7C III samples. I find that the density of the source environment is a strong function of the source radio–luminosity but is insensitive to changes in redshift. The jet power is also a strong function of radio-luminosity but also a weak function of redshift. This indicates that the mass of the black–hole powering FRII sources is epoch dependent. In general, I find that the source environment is domi- nated by changes in the radio–luminosity but is relatively unaffected by changes in cosmic epoch. CONTENTS –i– Contents 1 Introduction 1 1.1 Classifying radio galaxies . 2 1.2 EnvironmentorOrientation?. 3 1.2.1 TheLaing-Garringtoneffect . 4 1.2.2 Liu-Pooleyeffect ......................... 4 1.2.3 Evidence for a non uniform medium around radio galaxies . 4 1.2.4 X-ray ............................... 5 1.2.5 Galaxy correlation methods . 6 1.2.6 Alignmenteffect ......................... 7 1.2.7 SpectralAgeing.......................... 7 1.2.8 UnifiedModel........................... 8 1.2.9 Sourceorenvironment?. 9 1.3 Flux limited samples . 9 1.4 Modelling FRII’s and their environment . 10 1.5 Thiswork ................................. 11 1.6 Synopsis.................................. 12 CONTENTS –ii– 2 Observations 14 2.1 Observationalprogram . 15 2.1.1 Sample selection . 15 2.1.2 VeryLargeArrayobservations. 16 2.1.3 ObservationalPrograms . 18 2.2 DataReduction.............................. 22 2.2.1 Flux calibration. 22 2.2.1.1 Calibrating the primary calibrator. 23 2.2.1.2 Calibrating the secondary . 24 2.2.2 Polarisation calibration. 24 2.2.3 Calibration of source files . 25 2.2.3.1 Clean . 25 2.3 Mapproduction.............................. 26 2.3.1 Notes on individual sources . 28 2.3.1.1 SampleA:........................ 28 2.3.1.2 SampleB:........................ 31 2.3.1.3 SampleC:........................ 32 3 Trends 35 3.1 PolarisedFluxandSpectralIndex. 36 3.2 Rotationmeasure ............................. 36 3.3 Depolarisation............................... 41 3.3.1 Laing–Garringtoneffect . 47 CONTENTS –iii– 3.3.2 Depolarisation shadows . 48 3.4 UsingBurn’slaw ............................. 49 3.4.1 Polarisation . 49 3.4.2 Depolarisation . 49 3.5 Discussion................................. 52 4 Analysing the observations 54 4.1 Statistics.................................. 55 4.1.1 SpearmanRank.......................... 55 4.1.2 Principal Component Analysis, PCA . 56 4.2 FundamentalParameters. 56 4.3 ObservationalParameters . 58 4.3.1 Spectralindex........................... 58 4.3.2 Depolarisation . 59 4.3.3 Rotationmeasure......................... 62 4.3.4 Summary ............................. 65 4.4 Sourceasymmetries............................ 66 4.4.1 Fluxasymmetries......................... 67 4.4.2 Asymmetriesinspectralindex . 69 4.4.2.1 Liu-Pooley effect . 69 4.4.2.2 Effect of changes in the lobe length . 71 4.4.2.3 Minimum energy of the magnetic field . 72 4.4.3 Asymmetries in depolarisation . 75 CONTENTS –iv– 4.4.4 Asymmetries in σRMz ....................... 76 4.4.5 Summary ............................. 77 4.5 Conclusions ................................ 78 5 Modelling of the Faraday screen 80 5.1 CritiqueofBurn’smodel ......................... 81 5.2 TheTribblemodels............................ 82 5.2.1 Quadraticmodel ......................... 82 5.2.2 Gaussianauto-correlationmodel. 83 5.2.3 Power-lawmodel ......................... 84 5.2.3.1 Powerlawexponent . 84 5.3 Fitting the T91 models to the observations . 84 5.3.1 Constant s◦, constant σRM .................... 86 5.3.2 Varying s◦ and σRM ....................... 86 5.3.3 Depolarisation . 88 5.3.3.1 Constant s◦, constant σRM ............... 88 5.3.3.2 Varying s◦ and σRM .................. 89 5.3.4 Scatter in s◦ ............................ 90 5.3.5 Using s◦=10kpc ......................... 91 5.4 Conclusions ................................ 92 6 Modelling FR II sources 94 6.1 ThemodelforFRIIsources . 95 6.1.1 Application of the model . 97 CONTENTS –v– 6.2 Modelling the small sample . 98 6.2.1 Angle to the line of sight . 99 6.3 Results................................... 99 β 6.3.1 Comparing a◦ ρ◦ with DMz and σRMz ..............100 β 6.3.2 Minimum energy, a◦ ρ◦ and plobe .................102 6.4 Modelling the complete 3CRR, 6CE and 7C III FRII samples . 103 6.4.1 Observations ...........................103 6.4.2 Application of the model to the combined sample . 103 6.4.3 FundamentalParameters. .104 6.4.4 Sourceage,ty...........................106 6.4.5 Lobe pressure, plobe ........................108 β 6.4.6 Density of the source environment, a◦ ρ◦ ............111 6.4.7 Jet power, Q◦ ...........................112 6.5 Conclusions ................................114 7 Conclusions 116 7.1 EvolutionoftheFaradayscreen . .117 7.2 FurtherWork ...............................118 A Sample A maps 120 B Sample B maps 121 C Sample C maps 122 D Cosmology 123 CONTENTS –vi– D.1 Basicassumptionsused. .123 E 3CRR sample 124 F 6CE sample 129 G 7C III sample 132 LIST OF FIGURES –vii– List of Figures 1.1 CygnusA ................................. 3 1.2 UnifiedModel............................... 8 1.3 A radio luminosity-redshift plot for the 3CRR sample . 10 1.4 AsimpleimpressionofaFRIIsource . 11 2.1 A radio luminosity-redshift plot for the 3 subsamples. 15 2.2 Linear size-redshift plots of the 3 subsamples. 16 2.3 7C1745+642:anexampleofflagging . 23 2.4 Rotationmeasurefitsfor6C1256+36. 30 2.5 Rotationmeasurefitsfor4C16.49. 33 3.1 Plot of the Faraday dispersion, against the rms of the rotation mea- sureforeachsource. ........................... 43 3.2 Average depolarisation against projected linear size . 48 3.3 Exampleofadepolarisationshadow. 49 4.1 Redshift-sizerelation ........................... 57 4.2 Redshift and radio-luminosity against DMz ............... 60 4.3 DMz against the difference in depolarisation, dDMz........... 61 4.4 dRMz againstredshift .......................... 63 LIST OF FIGURES –viii– 4.5 Rotationmeasurevariations . 65 4.6 Fluxes of the brightest to faintest lobe . 67 4.7 Flux ratio against lobe ratio . 68 4.8 Flux ratioagainstthe fundamental parameters . 69 4.9 Liu-PooleyeffectI............................ 70 4.10Liu-PooleyeffectII ........................... 70 4.11 The ratio of spectral indices against the lobe ratio. 71 4.12 α ratioagainstfluxratio ......................... 71 4.13 α ratioagainstloberatio......................... 72 4.14 The minimum energy magnetic field ratio against flux and α ratios . 73 4.15 The minimum energy magnetic field ratio against z . 74 4.16 The minimum energy magnetic field ratio against DM & σRMz ratios 74 4.17 Depolarisation of the brightest to faintest lobe . 75 4.18 Depolarisationasymmetries . 76 4.19 σRMz ofthebrightesttofaintestlobe . 77 4.20 σRMz asymmetries ............................ 77 5.1 Tribble model for constant s◦ and σRM ................. 87 5.2 Tribble models for varying s◦ and σRM ................. 87 5.3 Tribble models for varying m, the exponent of the Power law model . 88 5.4 Tribble model predictions for the depolarisation I . 89 5.5 Tribble model predictions for the depolarisation II . 89 5.6 Tribble model predictions for the depolarisation III . 90 5.7 Effects of varying s◦ ............................ 91 LIST OF FIGURES –ix– β 6.1 Relationship between depolarisation and a◦ ρ◦ .............100 β 6.2 Relationship between σRMz and a◦ ρ◦ ..................101 β 6.3 Relationship between redshift and radio luminosity with a◦ ρ◦ . .101 β 6.4 Relationship between σRMz and a◦ ρ◦ ..................102 6.5 Redshift against the radio luminosity at 151 MHz for the combined sample...................................104 6.6 Relationship between z, P151 MHz & Dlobe.................105 6.7 Age of a source in relation to radio size
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