During the quasar era (redshifts between 1 and 3) Radio Galaxies (RGs) have been claimed to have substantially influenced the growth and evolution of large scale structures in the universe. In this dissertation I test the robustness of these exciting claims. In order to probe the impacts in more detail, good theoretical models for such RG systems are required. With this motivation, I seek to develop an essentially analytical model for the evolution of Fanaroff-Riley Class II radio galaxies both as they age individually and as their numbers vary with cosmological epoch. To do so, I first compare three sophisticated semi-analytical models for the dynamical and radio lobe power evolution of FR II galaxies, those given by Kaiser, Dennett-Thorpe & Alexander (1997, KDA), Blundell, Rawlings, & Willott (1999, BRW) and Manolakou & Kirk (2002, MK). I perform multi-dimensional Monte Carlo simulations leading to virtual radio surveys. The predictions of each model for redshift, radio power (at 151 MHz), linear size and spectral index are then compared with data. The observational samples are the low frequency radio surveys, 3CRR, 6CE and 7CRS, which are flux-limited and redshift complete. I next perform extensive statistical tests to compare the distributions of model radio source parameters and those of the observational samples. The statistics used are the 1-Dimensional and 2-Dimensional Kolmogorov-Smirnov (K-S) tests and the 4-variable Spearman partial rank correlation coefficient. I search for and describe the "best" parameters for each model. I then produced modifications to each of the three original models, and extensively compare the original and the modified model performances in fitting the data. The key result of my dissertation is that using the Radio Luminosity Function of Willott et al. (2001) as the redshift birth function of radio sources, the KDA and MK models perform better than the BRW models in fitting the 3CRR, 6CE and 7CRS survey data when using K-S based statistical tests, and the KDA model provides the best fits to the correlation coefficients. However, no pre-existing or modified model can provide adequate fits for the spectral indices. I also calculate the volume fraction of the relevant universe filled by the generations of radio galaxies over the quasar era. This volume filling factor is not as large as estimated earlier. Nonetheless, the allowed ranges of various model parameters produce a rather wide range of astrophysically interesting relevant volume fraction values. I conclude that the expanding RGs born during the quasar era may still play significant roles in the cosmological history of the universe.

Magister Scientiae - MSc / We investigate the modelling of radio galaxies within a semi-analytic framework in the Millennium Simulation of the Virgo Consortium. The aim is to assess the radio sources contamination of Sunyaev-Zeldovich (SZ) signatures of clusters of galaxies in Cosmic Microwave Background (CMB) experiments. The modelling is also relevant to the Karoo Array Telescope (MeerKAT) and the Square Kilometre Array (SKA) science. The semi-analytical model consists of N-body simulation, the Millennium Run to trace the merger history of dark matter haloes within the Λ Cold Dark Matter (ΛCDM) cosmology and a follow up of the black hole accretion history and Active Galactic Nuclei (AGN) evolution. We study the growth of the supermassive black hole (SMBH) in galaxy centres and determine the black hole mass accretion conversion into radiation. We identify a model which matches observed radio luminosity function. We describe a model of observed sample of radio surveys at a given frequency and a flux density limit to obtain a model of radio luminosity function (space density of radio sources as a function of redshift) that we compare with our simulated data. We determine the redshift distribution of radio galaxies (FRI), blazars and radio quasars (FRII) in the simulation. We focus the modelling on flat spectrum population of blazars since their jets are collimated towards us and thus constitute the most potential contaminants of the CMB. We determine the spatial and density distribution of radio sources in clusters with a virial mass Mvir 2 1014h−1M and then compute the temperature fluctuations and fluxes produced by these cluster radio sources. Our main results include: the model provides a reasonable match within uncertainties with the model obtained by Dunlop & Peacock (1990) [39] using their best fit of radio luminosity function at redshift z . 0:3. The model underestimates the number of radio sources at high redshift z & 1. Radio sources are concentrated around the centre of clusters with a maximum density at r . 0:1r200 where r200 is the radius within which the density is 200 times the critical density. Radio sources are more concentrated in low mass clusters. The model predicts a surface density profile of radio sources with luminosity P 1023 W.Hz−1 at 1.4 GHz (z . 0:06) in agreement with that of Lin & Mohr (2007) [58] at r . 0:1r200 but underestimates the density in the outskirts of the clusters. BL Lacs and FRI radio galaxies produce non negligible contamination at redshift z . 0:1. They produce a mean temperature fluctuation 4:5 K at redshift z 0:01 which can be at the same level as the kinetic SZE signal produced by the cluster. Blazars constitute potential contaminant of the thermal SZ effect at redshift z 1:0 and z 1:5 at 145 GHz where they produce a mean temperature 300 K - 350 K for an average mass of the cluster. / South Africa