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Title: Jets, hotspots and lobe morphology in radio galaxies and quasars
Author: Gilbert, G.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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This thesis concerns the radio structure of FR II radio galaxies and quasars on kiloparsec scales. A complete sample of 65 FR II sources with redshift < 0.6 is examined with the aim of understanding the source characteristics. High sensitivity, high resolution images of 27 FR II sources are presented forming a complete subsample with 0.3 < z < 0.6; for each source the morphological features are discussed in detail and general trends within the sample are noted. The observed asymmetries between the two sides in each source are analysed. At first, these are interpreted as a result of relativistic orientation effects and comparisons are made between the observed data and theoretical models. Correlations between observable parameters of the quasars and radio galaxies are examined separately but few are found to be consistent with orientation-dependent unification schemes between the two classes; it is clear that environmental effects must be dominate in most sources. The reliability of measurements of hotspot linear sizes is discussed. Hotspot location relative to the lobe is found to be broadly consistent with orientation unification schemes. The apparent recession of hotspots however is shown to be inconsistent with purely geometrical effects. The relatively large number of highly recessed hotspots suggests that in at least some cases what we classify as a hotspot cannot be a feature that is associated with the termination point of the beam. The general morphology of lobes and the importance of self-similar expansion is reviewed. Axial ratio is regarded as a fundamental structural parameter and observational values compared to models of source evolution. The model of self-similar expansion due to Kaiser and Alexander (1997) is developed to give an analytical expression for lobe axial ratio. Fits are made to the data and are in remarkable agreement with observed values.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available