A low frequency survey of radio sources

The dissertation describes work carried out as part of the 6th Cambridge survey of cosmic radio sources (the 6C Survey). The survey was made at an observing frequency of 151 MHz, with an angular resolution of 4 arcmin. The first chapters describe the nature of the survey and the data reduction procedure for the strip of sky centred on declination 58 degrees, for which the author was responsible. The survey records themselves are not presented with the thesis because of their bulk but they will later be published in a more suitable form. There is an account of an investigation into the effect of irregular ionospheric refraction on the operation of the 151 MHz telescope and a demonstration of a method for reducing its effects on maps. The main part of the thesis consists of analyses based on the data from the 6C survey: 1) A study of the isotropy of the distribution of the radio sources in the 6C catalogue. A powerful test for clustering is developed and the weakest sources are shown to be uniformly distributed, although there is a hint of clustering amongst the stronger objects. 2) A statistical study of the weak, low-brightness objects found in the survey shows that their distribution is in agreement with predictions based on a sample of stronger radio sources (the 3CR sample). 3) Several individual interesting objects observed in the course of the survey have been investigated in detail and a discussion of these is presented. Finally there is a description of a statistical study of the cosmological evolution of flat-spectrum quasars found in the course of the Parkes 2.7 GHz survey. The results of a V/Vsub(m) analysis showed that their evolution was much less than that shown by the steep-spectrum samples studied previously, a result which has since been confirmed by several other investigators. (author)