Very steep spectrum radio sources and clusters of galaxies
The topics covered in this dissertation are all areas of study involving observations at low radio frequencies. There are three main subject areas: a study of the twin-tailed radio galaxy 3C3.1; a study of both an old and a new sample of radio sources that exhibit very steep radio spectra at low frequency; the design and construction of a new radio telescope operating at low radio frequency together with the making of a new radio source survey. 3C3.1 has been studied by other authors but new high angular resolution, high sensitivity observations at low radio frequency have allowed further progress to be made in understanding the behaviour of this source. It has been thought that 3C3.1 type sources would be responsible for most (if not all) of the very steep spectrum radio sources. 3C3.1 is relatively close, hence easy to study. A model has been developed which explains the previously not understood brightness distribution along the long luminous jets. In order to quantify the predicted behaviour more precisely a set of simple numerical simulations was performed. Very steep spectrum radio sources are by their nature easier to detect at low radio frequencies. In the past, it has been shown that most, if not all, very steep spectrum sources are associated with clusters of galaxies. Both optical and further radio observations of a sample of sources prepared by the author, and a sample prepared by other workers were undertaken. The optical observations of high sensitivity have greatly strengthened the hypothesis that all of such sources are indeed associated with clusters of galaxies. The radio observations, both performed at high and low radio frequencies, have shown that such sources seem to have in general evolved from conventional sources with both 'tailed' and 'double' radio structure. A serious limitation for further work at low radio frequencies is the availibility of high sensitivity, high resolution instruments. A twenty five element interferometer with a one mile baseline operating at 38 MHz was designed and constructed. This allowed an appraisal of the operating conditions at such low frequency. A deep radio survey of the north pole was performed and a new sample of very steep spectrum constructed.