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Title: Radio galaxies as large-scale cosmological probes
Author: Nicholson, David
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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An all-sky sample of essentially all the radio galaxies within 30000kms-1 down to a flux-density limit of about 0.5Jy at 1.4GHz is assembled from the Parkes, Bologna, Jodrell Bank and Bonn surveys. The ease and uniformity with which this class of object can be selected render them as excellent statistical probes of the large-scale structure. This thesis is concerned with an application of the sample to study clustering and streaming motions in the universe on 10-100h-1 Mpc scales. The observational database acquired for the radio galaxies comprise spectroscopic redshifts and I band CCD frames, with additional B frames for a few of the galaxies. These allow a simple distance indicator relation for the radio galaxies to be derived by fitting de Vaucouleurs empirical r(1/4) law to the azimuthally-averaged surface brightness profiles of the galaxies. This yields an effective size parameter rePROB*LEM and a distance-independent surface-brightness μ for calibrating the 'standard rods'. In terms of rms scatter, the μ-rePROB*LEM relation yields relative distance accurate to about 28%. This compares favourably with other distance indicators which incorporate velocity dispersions, yet it has the advantage that the photometric parameters μ and r_ePROB*LEM are very straightforward to measure. A useful parameter describing the richness of the environments of radio galaxies is the amplitude of the spatial cross-correlation function B_grPROB*LEM. Its calculation in the past has involved using full sets of galaxy counts, notably the Lick counts to do the cross-correlation. In the absence of such a set of galaxy counts, for declinations south of -23^o, it is shown that the Abell cluster catalogue can be used to obtain a reasonable estimate of B_grPROB*LEM. Considering the all-sky sample as a whole it is found that, on average, radio galaxies reside in systems of Abell richness R imeq 0. A search for correlations between radio luminosity and B_grPROB*LEM for the radio galaxies is performed but none are found. Similarly, no evidence is found for correlations between optical luminosity and B_grPROB*LEM. The 3-d correlation function for radio galaxies is calculated here for the first time. A strong signal is detected, although not as strong as some reports in the past of the cluster-cluster correlation function would have suggested. There is no trend for the clustering signal to show a systematic increase or decrease if radio galaxies in bands of radio luminosity are considered separately. No evidence is found to support the claim by Tully that rich clusters are aligned along the supergalactic plane and exhibit correlated structure on a scale 0.1c.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available