Bibliography : leaves 1-6 of 2nd sequence / vii, 104, [28] 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.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1993

Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1993. / Includes bibliographical references (leaves 1-6 of 2nd sequence).

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Richard Matzner. Vita. Includes bibliographical references. Available also from UMI company.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xx, 198 p.; also includes graphics (some col.). Includes bibliographical references (p. 191-198). Available online via OhioLINK's ETD Center.

Using the Chandra X-ray Observatory, Martini et al. (2006) found that the AGN fraction of galaxy clusters was five times higher than previous optical studies suggested. Using visual observations only, Dressler et al. (1985) estimated the AGN fraction of field galaxies to be 5%, while that of clusters was thought to be 1%. To understand the role that the environment plays in AGN fueling, the author studied a variety of environments, ranging from the field to groups to clusters. Will the AGN fraction of groups also be higher than that of the field? The author demonstrates how the AGN fraction of groups compares to that of clusters. In the following sections, the author describes the mechanics of X-ray astronomy, the group environment, and the characteristics of active galactic nuclei. The author briefly describes the possible mechanisms for AGN fueling.

A small fraction of cosmic microwave background (CMB) photons scatter off electrons in the ionised gas in collapsed structures. This process, known as the Sunyaev-Zel'dovich effect, is usually broken down into a thermal (tSZ) and a kinematic (kSZ) contribution. While the former is sensitive to the random velocities of the electrons in the hot gas, the latter is sourced by the bulk motion of the entire object. In this thesis I measure the signature of both of these effects by cross-correlating CMB data with different tracers of the large-scale structure. I further study how these effects can be used as probes of cosmology and astrophysics. I first report a statistically significant detection of the kSZ effect. This is achieved by combining a cluster catalogue derived from the first year data of the Dark Energy Survey with CMB temperature maps from the South Pole Telescope. I perform the measurement with a differential statistic that isolates the pairwise kSZ signal, providing the first detection of the large-scale motion of clusters using redshifts derived from photometric data. By fitting the pairwise kSZ signal to a theoretical template, I measure the average central optical depth of the cluster sample. I compare the extracted signal to simulations and find good agreement with respect to the signal-to-noise, the constraint on the optical depth, and the corresponding gas fraction. I next study the potential of the kSZ effect as a probe of cosmology, again focussing on the pairwise method. The main challenge is disentangling the cosmologically interesting mean pairwise velocity from the cluster optical depth and the associated uncertainties on the baryonic physics in clusters. Using the Magneticum cosmological hydrodynamical simulations I calibrate a scaling relation between the amplitude of the tSZ signal and the optical depth. I show that this relation can be used to recover an accurate estimate of the mean pairwise velocity from the kSZ signal, and that this effect can therefore be used as a probe of cosmology. I finally derive constraints on feedback from active galactic nuclei by setting limits on their tSZ signal. By combining all-sky microwave, sub-mm, and far-infrared data from the Planck and AKARI satellites, I break the degeneracy between the tSZ signature and extragalactic dust emission. I test the measurement pipeline with a catalogue of galaxy clusters, finding the expected high-significance tSZ detection together with correlated dust emission. I then measure the tSZ signal of spectroscopically confirmed quasi-stellar objects (QSOs), but obtain only a low-significance hint of a tSZ signature. This analysis leads to a lower mean thermal energy than reported in some previous studies which were contaminated by dust emission. A comparison of these results to hydrodynamical simulations can be used as a probe of QSO host masses.

Contemporary projects to measure anisotropies in the cosmic microwave background (CMB) are now detecting hundreds to thousands of extragalactic radio sources, most of them blazars. As a member of a group of CMB scientists involved in the construction of catalogues of such sources and their analysis, I wish to point out the potential value of CMB surveys to studies of AGN jets and their polarization. Current CMB projects, for instance, reach mJy sensitivity, offer wide sky coverage, are blind and generally of uniform sensitivity across the sky (hence useful statistically), make essentially simultaneous multi-frequency observations at frequencies from 30 to 857 GHz, routinely offer repeated observations of sources with interesting cadences and now generally provide polarization measurements. The aim here is not to analyze in any depth the AGN science already derived from such projects, but rather to heighten awareness of their promise for the AGN community.

Masters of Science / The study of the faint radio universe and of its properties has recently become a very active field of research not only because of the much improved capabilities of the SKA pathfinders but also because of the need to better plan for SKA surveys. These new facilities will map large areas of the sky to unprecedented depths and transform radio astronomy into the leading technique for investigating the complex processes which govern the formation and evolution of galaxies. This thesis combines multi-wavelength techniques, highly relevant to future deep radio surveys, to study the properties of faint radio sources. The nature of the faint radio sources is presented, over a large GMRT survey area of an area of 1.2 deg2 comprising 2800 sources. Utilising multi-wavelength data we have matched 85% of the radio population to Spitzer/IRAC and obtained a redshift estimate for 63%. The redshift associations are a combination of photometric and spectroscopic redshift estimates. This study investigates several multi-wavelength diagnostics used to identify AGN, using radio, infrared, optical and x-ray data . This analysis shows that various diagnostics (from the radio through the X-ray ones) select fairly different types of AGNs, with an evidence of a disagreement in the number of AGNs selected by each individual diagnostics. For the sources with redshift we use a classification scheme based on radio luminosity, x-ray emission, BOSS/SDSS spectroscopy, IRAC colors satisfying the Donley criterion, and MIPS 24ɥm radio-loud AGN criteria to separate them into AGNs and SFGs. On the basis of this classification, we find that at least 12.5% of the sources with redshifts are AGNs while the remaining 87.5% are adopted as SFGs. We explore the nature of the classified sources through the far-infrared radio correlation. We measure a median qIR value of 2:45± 0:01 for the SFGs and qIR value of 2:27 ± 0:05 for the AGNs. The decrease in the median value of qIR for the AGNs is a result of the additional AGN component to radio emission for the AGN-powered sources and find tentative evidence of an evolution of the qIR with redshift.

Les Noyaux Actifs de Galaxies (AGN) se situent au centre de galaxies extrêmement lointainesdont la luminosité provient de l’interaction d’un trou noir central supermassif et d’undisque d’accrétion. Il en résulte l’éjection à des vitesses relativistes de jets de matière collimatés.L’interférométrie à très longue base (VLBI) permet, grâce aux très grandes résolutionsatteintes, d’observer finement la structure de ces jets et de déterminer très précisément laposition astrométrique des objets. En raison de leur distance, les AGN ne présentent pas demouvements propres, ce qui les rend idéaux pour la construction de systèmes de référenceultra-précis et très stables.Des instabilités en position de quelques centaines de microsecondes d’arc, généralementimputées aux variations de la structure des jets, sont toutefois souvent observées sur des échellesde temps de quelques mois à quelques années. Le travail présenté ici étudie le lien entre les deuxphénomènes de façon statistique. Sur la base d’observations VLBI régulières conduites entre1994 et 2003, nous comparons l’évolution de la position astrométrique et de la structure des jetspour un échantillon de 68 AGN sur une période de 10 ans. Les résultats de l’étude indiquent quela corrélation entre les deux phénomènes existe mais n’est pas aussi forte qu’attendue. Le travailest complété par une simulation des effets causés sur la trajectoire des jets par la précessiondu disque d’accrétion ainsi que par la présence d’un système binaire de trous noirs. Appliquéeau cas de la source 1308+326, l’étude montre que l’amplitude de ces effets est compatible avecles oscillations de la trajectoire observées en VLBI. / Active Galactic Nuclei (AGN) are located in the center of extremely distant and bright galaxies. Their luminosity comes from the interaction between a super-massive central blackhole and an accretion disk, producing a relativistic collimated jet of matter. Thanks to the extremely high resolution achieved by Very Long Base line Interferometry (VLBI), the jet structure may be studied in detail, while the astrometric position of the AGN is determined with ahigh accuracy. Because of their location at cosmological distances, no proper motions are detected for those objects, making them ideal fiducial points for building highly-precise celestial reference frames.Instabilities up to a few hundreds of micro arc seconds are yet often observed in astrometricpositions on time scales from months to years. This is generally thought to be caused by theevolution of source structure. The study presented here investigates the correlation between the two phenomena on a statistical basis. Based on regular VLBI observations conducted between1994 and 2003, astrometric position variations and source structure evolution are compared fora sample of 68 AGN over a period of 10 years. The results indicate that a correlation between the two phenomena does exist but it is not as strong as expected. Additionally, a simulation of the effects caused by the precession of the accretion disc and the potential presence of abinary black hole in the center of the AGN is presented. Applied to the source 1308+326, the simulation shows that the magnitude of the effects is consistent with the oscillations of the jet trajectory observed on VLBI scale.