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Title: Cosmological tests of unified models for extragalactic radio sources
Author: Jackson, C. B.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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This thesis considers if the current 'unified scheme' for powerful extragalactic radio sources are valid in the light of cosmological tests embodied in radio source count and identification data. Although the analysis is based on the simplest possible parametric descriptions of radio source evolution and beaming, the overall agreement with the available observational data is quite remarkable. The first part of the thesis describes an identification programme of flat-spectrum radio sources at 2.7 GHz. The complete sample provides two important pieces of information (1) whether a turnover in the space density of quasars as a function of redshift can be determined (2) the nature of the flat-spectrum galaxies in the sample which must be understood in the context of the current unified scheme. A statistical analysis of the space-density evolution of the powerful radio sources is then performed, adopting simple parametric descriptions of the evolution to fit a low-frequency radio source count. The analysis uses a coherent description of the known radio source populations such that the space density evolution of the powerful radio sources can be established. The successful space density models are scrutinized to ensure that these unified scheme-based predictions are reconcilable with all available data, which includes the observed turnover in space density of the FRII population from the 2.7-GHz flat-spectrum sample. The successful space density evolution model is then applied to the 5-GHz source count where the contribution from Doppler-beamed, flat-spectrum, sources is significant. The unified scheme posits that the beamed products have the same evolution histories as their underlying 'parent' sources, so that the space density model is valid at all radio frequencies. Simple parametric descriptions of the Doppler beaming are applied to the powerful radio source populations to produce their respective flat-spectrum products.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available