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Title: The dynamics and energetics of radio-loud active galaxies
Author: Harwood, Jeremy James
ISNI:       0000 0004 5347 9692
Awarding Body: University of Hertfordshire
Current Institution: University of Hertfordshire
Date of Award: 2014
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In this thesis, I use the new generation of radio interferometer along with X-ray observations to investigate the dynamics and energetics of radio-loud active galaxies which are key to understanding AGN feedback and the evolution of galaxies as a whole. I present new JVLA observations of powerful radio source and use innovative techniques to undertake a detailed analysis of JVLA observations of powerful radio galaxies. I compare two of the most widely used models of spectral ageing, the Kardashev-Pacholczyk and Jaffe-Perola models and also results of the more complex, but potentially more realistic, Tribble model. I find that the Tribble model provides both a good fit to observations as well as providing a physically realistic description of the source. I present the first high-resolution spectral maps of the sources and find that the best-fitting injection indices across all models take higher values than has previously been assumed. I present characteristic hot spot advance speeds and compare them to those derived from dynamical ages, confirming that the previously known discrepancy in speed remains present in older radio sources even when ages are determined at high spectral and spatial resolutions. I show that some previously common assumptions made in determining spectral ages with narrow-band radio telescopes may not always hold. I present results from a study of the powerful radio galaxy 3C223 at low frequencies with LOFAR to determine its spectrum on spatially small scales and tightly constrain the injection index, which I find to be consistent with the high values found at GHz frequencies. Applying this new knowledge of the low energy electron population, I perform synchrotron / inverse-Compton model fitting and find that the total energy content of the radio galaxy lobes increases by a factor greater than 2 compared to previous studies. Using this result to provide revised estimates of the internal pressure, I find the northern lobe to be in pressure balance with the external medium and the southern lobe to be overpressured. I go on to present the first large sample investigation of the properties of jets in Fanaroff and Riley type I radio galaxies (FR-I) at X-ray energies based on data from the Chandra archive. I explore relations between the properties of the jets and the properties of host galaxies in which they reside. I find previously unknown correlations to exist, relating photon index, volume emissivity, jet volume and luminosity, and find that the previously held assumption of a relationship between luminosities at radio and X-ray wavelengths is linear in nature when bona fide FR-I radio galaxies are considered. In addition, I attempt to constrain properties which may play a key role in determination of the diffuse emission process. I test a simple model in which large-scale magnetic field variations are primarily responsible for determining jet properties; however, we find that this model is inconsistent with our best estimates of the relative magnetic field strengths in my sample.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Radio galaxies ; X-ray jets ; active galaxies ; spectral ageing ; acceleration of particles ; non-thermal radiation mechanisms ; AGN ; data analysis methods ; radio continuum