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The results are presented here of multi-wavelength observations centred on two fields of the Leiden-Berkeley Deep Survey, which form the basis for a study of the population and cosmic evolution of the high redshift, low power, Fanaroff & Riley class I (FRI) radio galaxies. These fields, Hercules.1 and Lynx.2, contain a complete sample of 81 radio sources with S_1.4GHz > 0.5 mJy within 0.6 square degrees. Wide-field, ~1.5 arcsec resolution, radio observations, along with near infra-red and optical imaging, and some multi-object spectroscopy, are used to select the best high-redshift FRI candidates, giving 37 in total. Currently, the host galaxy identification fraction is 86% with 11 sources remaining unidentified at a level of r > 25.2 (Hercules; 4 sources) or r > 24.4 (Lynx; 7 sources) and K > 20. Spectroscopic redshifts are determined for 49% of the sample and photometric redshift estimates are presented for the sample sources without spectra or previously published results. 95% of the 37 best FRI high-redshift candidate sources were then observed using sub-arcsecond radio resolution, with the aim of detecting extended emission with respect to compact core features - vital for unambiguous morphological classification. The nature of the radio observations meant that 10 extra sample sources could also be included in the data. Lower resolution data were also taken for the Lynx.2 field sources to provide a comparison with the 1.5 arcsec data. The classification of the entire radio sample is done in two stages. Sources which showed clear extension are classified by morphology alone, whereas sources with no obvious or weak extension were classified using a combination of morphology and flux density loss in the higher resolution data indicative of resolved out extended emission. Five groups are used for this - 'Certain FRIs', 'Likely FRIs', 'Possible FRIs', 'Unclassifiable sources' (for those not included in the higher resolution observations) and 'Not FRIs'. The final group numbers are 8, 10, 24, 33 and 6 for groups 1-5 respectively. The space densities of the maximum, probable and minimum FRIs are then calculated and compared to two previously published measurements of the local value, and with the behaviour of the strongest FRII sources. The results for all three groups show density enhancements of factors of 5-9 at z ~ 1.0 which implies cosmic evolution of the FRI population; this enhancement is also in very good agreement with that predicted by previous models. The behaviour of the FRI/FRII dividing luminosity, as a function of host galaxy absolute magnitude, at the different cosmic epochs of the sample, and for two different star formation histories, is also investigated. A shift to brighter absolute magnitudes is found to be inconsistent with the data but this conclusion is weak due to the lack of knowledge of the host galaxy stellar populations, and the small number of sources in the sample.

The detection of Mpc scale diffuse radio emission in galaxy clusters provides evidence that cosmic ray electrons, as well as cluster scale magnetic fields are present in clusters. As such, radio observations of clusters provide a unique opportunity to study the non-thermal populations of the intra-cluster medium. Observations of Faraday rotation in sources embedded in cluster and group environments offers an additional method for probing the cluster/group magnetic field. In this thesis I present low frequency radio observations of multiple galaxy clusters in order to investigate the nature of diffuse radio emission present in many clusters. I also present observations of the giant radio galaxy NGC 6251 and discuss both the source properties as well as the host group environment. In Chapter 1 of this thesis I review the current understanding of galaxy clusters, groups and radio galaxies. I also describe some of the astrophysical processes important to this thesis. In Chapter 2 I discuss the interferometry and the process of calibrating interferometric data. I also describe some of the techniques used later in the thesis such as QUfitting and RM synthesis. In Chapter 3 I present my observations of the massive merging galaxy cluster MACSJ2243.3-0935. I report the discovery of a radio halo in MACSJ2243.3-0935, as well as a new radio relic candidate, using the Giant Meterwave Radio Telescope and the KAT-7 telescope. The radio halo is coincident with the cluster X-ray emission and has a largest linear scale of approximately 0.9 Mpc. I measure a flux density of $10.0\pm 2.0\, \rm mJy$ at 610 MHz for the radio halo. I discuss equipartition estimates of the cluster magnetic field and constrain the value to be of the order of $1\, \rm \mu G$. The relic candidate is detected at the cluster virial radius where a filament meets the cluster. The relic candidate has a flux density of $5.2\pm 0.8\, \rm mJy$ at 610 MHz. I discuss possible origins of the relic candidate emission and conclude that the candidate is consistent with an infall relic. In Chapter 4 I present my GMRT observations at 610 MHz of 3 disturbed galaxy clusters, A07, A1235 and A2055. No diffuse emision was observed any of the three clusters. In order to place upper limits on the radio halo power in these clusters I have injected simulated halos at difffent radio powers into the uvdata. A07 has a radio halo upper limit of $P_{\rm 610MHz}=1.5\times10^{24}$ W Hz$^{-1}$. A2055 has a radio halo upper limit of $P_{\rm 610MHz}=1.8\times10^{24}$ W Hz$^{-1}$. A1235 has a radio halo upper limit of $P_{\rm 610MHz}=5.8\times10^{23}$ W Hz$^{-1}$. These limits are below the $P_{610}-L_{\rm X}$ relation and rule out bright radio halo in these clusters. I have identified these clusters as potential hosts for Ultra Steep Spectrum Radio Halo (USSRH). Observations with LOFAR should be capable of confirming whether or not these clusters host USSRH. In Chapter 5 I present observations of the giant radio galaxy NGC 6251 with LOFAR HBA. NGC 6251 is a giant radio galaxy with a borderline FRI/FRII morphology located in a poor group. The images presented in this chapter are the highest sensitivity and resolution images of NGC 6251 at these frequencies to date. Analysis of the low frequencies spectral index did not reveal any change in the low frequency spectra when compared with the higher frequency spectral index. NGC 6251 is found to be either at equilibrium or slightly electron dominated, similar to FRII sources. I calculated the ages of the low surface brightness extension of the northern lobe and the backflow of the southern lobe, which are only clearly visible at these low frequencies, to be 205 Myr$.

Thesis (Doctoral)--Rijksuniversiteit Groningen, 2006. / Bibliography: p. [143]-158.

Thesis (M.Sc.)--Saint Mary's University, 2008. / Includes abstract and appendix. Supervisor: David Clarke. Includes bibliographical references (leaves 88-90).

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