The goal of this thesis is to develop an obscured AGN model for the X-ray background (XRB), and then to test the model via its predictions for the intensity of the cosmic background in the far infra-red, and by searching for obscured nuclei in individual X-ray sources in the near infra-red. A model invoking populations of obscured QSOs with a flat distribution of absorbing columns is found to give a good fit to the X-ray source counts and to the XRB spectrum. The model also accommodates the recent detection of a population of narrow-line X-ray galaxies, identifying them as low-luminosity obscured AGN. We investigate the selection effects present in optical QSO samples, and find that absorption in both the X-ray and optical wavebands combine to produce the tight observed X-ray/optical correlation, while still allowing a wide range of intrinsic column densities. X-ray sources with no obvious optical counterparts are predicted by this model, with a frequency in agreement with the numbers of these 'blank field' sources found in deep ROSAT surveys. We predict that in forthcoming AXAF surveys, ~ 50 per cent of the sources detected will be optically blank and lie at z (^>))(_~) 1. Obscured QSOs are estimated to outnumber unobscured QSOs by a factor of at least four to one. At longer wavelengths, we make a conservative prediction that obscured QSOs can account for approximately ten per cent of the sub-mm number counts and the far infra-red background, which is a modest, but non-negligible fraction. We then make observations to determine the extent of dust reddening in X-ray galaxies and QSOs, in the light of predictions of our obscured QSO model. We present K-band imaging of ROSAT and ASCA X-ray luminous galaxies and blank field sources. A trend is observed between the hardness of the X-ray spectra and the occurrence of red, unresolved counterparts, consistent with an obscured QSO origin for the X-ray emission. Near infra-red spectroscopy of X-ray luminous galaxies is then presented, searching for broad Pa(_a) emission lines. A broad line is possibly detected in one of six galaxies observed, which would indicate AGN activity. From far infra-red ISO photometry of X-ray galaxies and QSOs, we detect emission at ~ lOOμm from six narrow- line galaxies at low redshift, and from a Type 2 QSO at higher redshift. For at least two of the low redshift galaxies, there is clear proof of AGN activity on the grounds of X-ray variability and near infra-red spectroscopy. This, together with the 100μm detections, forms conclusive proof of the presence of dust-enshrouded AGN in at least some X-ray galaxies, supporting the obscured QSO explanation for the cosmic X-ray background.

In this Thesis we investigate the evolutionary histories of faint field galaxies using extremely deep optical and near-infrared photometry. Our work is centred on a 50 arcmin(^2) region at high galactic latitude which we call "The William Herschel Deep Field" (WHDF). In this work we describe three new near-infrared surveys of this field. In considering both this infrared data and the existing optical data, our broad aims are to increase our understanding of both the growth of galaxy clustering in the Universe and also to determine the star-formation histories of the field galaxy population. We consider our observations primarily in the context of luminosity evolution models in low density universes, but alternative scenarios are considered. Near-infrared galaxy counts derived from our catalogues are consistent with the predictions of our models, without the need for a steep faint-end slope for the galaxy luminosity function. We find that optical-infrared colour distributions of infrared-selected galaxies in the WHDF are deficient in red, early-type galaxies. This is consistent with the predictions of evolutionary models in which these systems have a small amount of on-going star-formation. We measure the amplitude of galaxy clustering in the WHDF for galaxies selected in optical and near-infrared bandpasses using the projected two-point correlation function. By comparing our measured clustering amplitudes with the predictions of our models we find that in all bandpasses the growth of galaxy clustering is approximately fixed in proper co-ordinates, again assuming a low-density Universe. Finally, an analysis of errors on the correlation function measurements suggest that discrepancies between our work and those of other authors may be explained by an underestimation of statistical errors.

In this thesis we investigate the two cosmic epochs of inflation and recombination, through their imprints on the temperature and polarization anisotropies of the cosmic microwave background radiation. To probe the early universe we develop a map-based maximum-likelihood estimator to measure the amplitude of inflation-induced gravity waves, parametrized by $r$, from the cosmic microwave background (CMB) polarization maps. Being optimal by construction, the estimator avoids $E$-$B$ mixing, a possible source of contamination in the tiny $B$-mode detection, the target of many current and near future CMB experiments. For various observational cases, we probe the dependence of $r$ measurement on the signal from different scales of $E$ and $B$ polarization. We make forecasts for Spider-like and Planck-like experimental specifications and to investigate the sky-coverage optimization of the Spider-like case. We also use a novel information-based framework to compare how different generations of CMB experiments reveal information about the early universe, through their measurements of $r$. We also probe the epoch of recombination by investigating possible fluctuations in the free electron fraction $\Xe$ around the fiducial model of the standard recombination scenario. Though theoretically well studied, the detailed assumptions in the recombination history, based on standard atomic physics, have never been directly tested. However, for our CMB-based cosmological inferences to be reliable, the recombination scenario needs to be observationally verified. We approach this problem in a model-independent way and construct rank-ordered parameter eigen-modes with the highest power to probe $\Xe$. We develop an information-based criterion to truncate the eigen-mode hierarchy, which can be used in similar hierarchical model selections as well. The method is applied to simulations of Planck+ACTPol and a cosmic variance limited survey with differing simulated recombination histories and recovered $\Xe$ trajectories are constructed. We apply the method to currently available CMB datasets, WMAP9+ACT/SPT. The first constructed eigen-mode turns out to be a direct measure of the damping envelope. Its current measurement with SPT slightly indicates a damping tail anomaly, while ACT data agree well with the standard scenario. High resolution Planck data will resolve this tension with high significance.

Our universe is inherently inhomogeneous yet it is common in the study of cosmology to model our universe after the homogeneous and isotropic Friedmann-Lemaıtre-Roberson-Walker (FLRW) model. In this thesis spacetime matchings are applied to investigate more general inhomogeneous cosmologies. The Cheese Slice universe, constructed from matching together FLRW and Kasner regions satisfying the Darmois matching conditions, is used as a prime example of an inhomogeneous cosmology. Some observational consequences of this model are presented. The lookback time verses redshift relation is calculated using a numerical algorithm and it is shown that the relative thickness of the Kasner regions have the greatest impact on anisotropies an observer would see. The number of layers and distribution of layers play a smaller role in this regard. The relative thickness of the Kasner slice should be on the order of one ten thousandth the thickness of the FLRW regions to have the anisotropies fall within the observed CMB limit. The approach to the singularity of a spacetime matching is examined. A criterion is presented for a matched spacetime to be considered Asymptotically Velocity Term Dominated (AVTD). Both sides of the matching must be AVTD and each leaf of the respective foliations mush match as well. It is demonstrated that the open and flat Cheese Slice universe are both AVTD and the singularity is also of AVTD type. The Cheese Slice model is then examined as a braneworld construction. The possibility of a Cheese Slice brane satisfying all the energy conditions is shown. However, the embedding of such a brane into a symmetric bulk is non-trivial. The general embedding of a matched spacetime into a bulk is investigated using a Taylor series approximation of the bulk. It is found that the energy-momentum tensor of such a brane cannot have discrete jumps if the embedding does not have a corner. A 3+1+1 decomposition of the bulk spacetime is then carried out. With the spacetime being deconstructed along two preferred timelike hypersurfaces, this becomes a natural environment to discuss the matching of branes. We find that there are conditions on the matter content of the branes to be matched if an observer on the brane is to see the matching surface as a boundary surface with no additional stress energy. Matching more than two bulks is also examined and shown to allow for more general brane configurations.

In this thesis we investigate the two cosmic epochs of inflation and recombination, through their imprints on the temperature and polarization anisotropies of the cosmic microwave background radiation. To probe the early universe we develop a map-based maximum-likelihood estimator to measure the amplitude of inflation-induced gravity waves, parametrized by $r$, from the cosmic microwave background (CMB) polarization maps. Being optimal by construction, the estimator avoids $E$-$B$ mixing, a possible source of contamination in the tiny $B$-mode detection, the target of many current and near future CMB experiments. For various observational cases, we probe the dependence of $r$ measurement on the signal from different scales of $E$ and $B$ polarization. We make forecasts for Spider-like and Planck-like experimental specifications and to investigate the sky-coverage optimization of the Spider-like case. We also use a novel information-based framework to compare how different generations of CMB experiments reveal information about the early universe, through their measurements of $r$. We also probe the epoch of recombination by investigating possible fluctuations in the free electron fraction $\Xe$ around the fiducial model of the standard recombination scenario. Though theoretically well studied, the detailed assumptions in the recombination history, based on standard atomic physics, have never been directly tested. However, for our CMB-based cosmological inferences to be reliable, the recombination scenario needs to be observationally verified. We approach this problem in a model-independent way and construct rank-ordered parameter eigen-modes with the highest power to probe $\Xe$. We develop an information-based criterion to truncate the eigen-mode hierarchy, which can be used in similar hierarchical model selections as well. The method is applied to simulations of Planck+ACTPol and a cosmic variance limited survey with differing simulated recombination histories and recovered $\Xe$ trajectories are constructed. We apply the method to currently available CMB datasets, WMAP9+ACT/SPT. The first constructed eigen-mode turns out to be a direct measure of the damping envelope. Its current measurement with SPT slightly indicates a damping tail anomaly, while ACT data agree well with the standard scenario. High resolution Planck data will resolve this tension with high significance.

230 leaves : ill. ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1981)--University of Adelaide, Dept. of Mathematical Physics, 1981

Doctor of Philosophy / This thesis presents a census of radio sources selected from the NRAO (National Radio Astronomy Observatory) VLA (Very Large Array) Sky Survey (NVSS) and Sydney University Molonglo Sky Survey (SUMSS) catalogues which have also been observed in the first data release of the 6 degree Field Galaxy Survey (6dFGS), a galaxy redshift survey of the local universe. Radio detections were found for 4,506 galaxies in the 6dFGS near-infrared-selected primary sample, a radio detection rate of 16%. A further 1,196 radio sources were observed by 6dF which were missing from the 6dFGS primary sample either because their host galaxies were too blue in colour or they appeared stellar on optical plates. The full sample comprises the largest and most homogeneous set of spectra and redshifts of radio sources in the local universe ever obtained. Results from the study of these objects form an accurate benchmark from which their cosmic evolution may be understood. 6dF spectra of galaxies have been used to determine the physical cause of radio emission from each object as either star formation or an active galactic nucleus powered by a super-massive black hole. These two classes of radio source have been characterised via a determination of the local radio luminosity function at 1.4 GHz; plotting the variation in their space density with luminosity. The star-formation density of the universe at the present epoch has been determined, the value of which which turns out to be in excellent agreement with previously published values. Fractional luminosity functions have also been determined showing that more massive galaxies have higher star-formation rates and are more likely to host a radio-loud AGN. The large-scale structure of star-forming galaxies and radio-loud AGN in the local universe has been studied by determining their clustering properties via the two-point correlation function. Radio-loud AGN are found to cluster more strongly than star-forming galaxies confirming that these objects are biased tracers of the underlying matter distribution. Both star-forming galaxies and AGNs cluster similarly to the underlying host galaxy population in which they reside. This thesis also describes the 843 MHz SUMSS catalogue, made by fitting elliptical Gaussians to sources in images. The catalogue contains radio sources to a limiting peak brightness of 6 mJy/beam at declination less than -50 degrees and 10 mJy/beam at declination greater than -50 degrees. Image artefacts have been classified using a novel technique involving a decision tree, which correctly identifies and rejects spurious sources in over 96% of cases and has ensured the catalogue is more than 95% complete and 90% reliable over most of its flux density range.

Thesis (M.A.)--Trinity Evangelical Divinity School, 1987. / Abstract. Includes bibliographical references (leaves 91-96).

Thesis (Ph.D. 1981)-- University of Adelaide, Dept. of Mathematical Physics, 1981.

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available online.