No description available.

To investigate the formation and evolution of galaxies a semi-analytic approach is adopted. This is based upon the Press-Schechter formalism, which provides a simple yet very powerful method for describing the distribution of dark matter haloes. An extension to the original formalism to examine merging haloes is described and simple assumptions are made to relate the haloes to the stellar component of the galaxy. This enables luminosity functions to be constructed to calculate source counts and to describe the three-dimensional distribution of galaxies. In addition, the production of heavy elements and the history of star-formation can also be inferred. The optical and near-infrared waveband number counts and redshift distribution were examined first, as a test of the model. These wavebands have been studied extensively, particularly in the optical waveband where observations of the Hubble Deep Field have detected galaxies to very faint magnitudes. The conclusion of this analysis is that extra luminosity evolution in the form of an epoch dependent star-formation efficiency is required by the model. An appropriate empirical form for this efficiency is adopted, which was constrained by the recent submillimetre observations that describe the dusty star-forming galaxies. This enabled a good description of the observed properties of these systems over the whole millimetre to ultraviolet waveband to be produced. Finally, the efficiency of star formation inferred from the dusty submillimetre galaxies was investigated. This used a combination of the Press-Schechter formalism and the model of chemical evolution as prescribed by Pei and Fall. Using only very general assumptions about the cooling and abundance of interstellar gas, an analytic form for the efficiency was derived which was very close to the empirical form found previously. Furthermore, the method used to derive the efficiency could be generalised to include different models of galaxy formation and also provide plausible scenarios for the evolution of active galactic nuclei.

Many galaxies in the Universe show evidence of a supermassive black hole at their dynamical centre. About 10-20% of these galaxies also contain an extremely bright, point-like continuum source in their nuclear region. These luminous objects are called active galactic nuclei (AGN), and are thought to be powered by material accreting onto the central black hole. The infalling gas loses its energy and angular momentum by passing through an accretion disc. The disc then radiates away this energy, and it is this radiation that is observed as an AGN. When observed in the X-ray waveband AGN are found to be very bright and rapidly variable (on timescales as small as 1000 s), implying that the emission must originate from the innermost regions of the central engine. X-ray spectra of AGN often exhibit distinct features that are attributed to radiation reflecting off of the accretion disc. Therefore, it is possible to use sensitive X-ray spectroscopic observations of AGN to directly probe the physics of accretion flows only a short distance away from the black hole. Comparing the results from AGN with different properties, such as luminosity or radio power, may allow general conclusions on the AGN phenomenon to be drawn. This thesis applies computations of X-ray reflection spectra to observations of different AGN in order to determine various properties of their accretion flows. The calculations take into account the ionization effects of the incident radiation and consider different density structures for the surface of the accretion disc. It was found that the model spectra were a good description of the observed X-ray data for many AGN between 1 and 10 keV. In particular, five narrow-line Seyfert 1 galaxies were well fit with reflection spectra from a highly ionized accretion disc, consistent with the idea that they contain rapidly accreting black holes. A similar result was found when fitting the data of 3C 120, a broad-line radio galaxy, which argues against the claim that radio-loud AGN have truncated accretion discs. On the other hand, a weakly ionized reflector proved to be a better fit to the Seyfert 1 galaxy MCG-6-30-15.

In this thesis, I develop a new method of treating the problem of radiative transfer around a forming massive star. This new method addresses the failings of grey radiative transfer through dusty gas, while avoiding the computational cost of frequency dependent transfer algorithms. My new algorithm is validated by comparison with previous frequency dependent calculations. This method is then applied to collapses of spherically symmetry gas clouds. I use this to show that there is no absolute radiative limit to stellar masses. Radiative feedback on the dusty inflow will cause a star to stop accreting, but this does not occur at any particular fixed mass. However, applying my new method to the Bondi-Hoyle geometry (likely to be found in a competitively accreting stellar cluster), I show that radiative feedback can still cause great difficulties in forming massive stars. The decreased central concentration, and presence of centrifugal support mean that radiative feedback can disrupt the Bondi-Hoyle flow. Although lack of time prevented me from exploring much parameter space, I am able to suggest the regions which might be fruitfully explored in the future.

No description available.

No description available.

Galactic chemical evolution models require stellar nucleosynthesis yields as input data. Stellar evolution models are used to calculate such yields but do not take into account the fact that many stars are in binaries. The computing time required to explore the binary star parameter space is usually considered to be prohibitively large. Therefore binaries, except for type Ia supernovae and novae which are included in an ad hoc way, are ignored in most galactic chemical evolution models. In this dissertation synthetic nucleosynthesis models are developed which approximate full stellar evolution models. Cunning methods are employed to model shell burning in low- and intermediate-mass stars while high-mass stars have their surface abundances fitted to their mass. Explosive yields are fitted to published results. The synthetic nucleosynthesis model, with the addition of algorithms to deal with mass transfer in binaries, is coupled to a rapid binary star evolution code. The use of a synthetic model speeds up the calculation of stellar yields by a factor of about 10⁷ and extends the analysis to binary stars. Single- and binary-star yields are calculated for a range of initial mass and separation distributions. A change in the primary or single-star mass distribution is most significant. Changing the secondary mass or separation distribution has a smaller effect. Consideration is then given to variation of the input physics to determine which free parameters are important for the calculation of yields from single and binary stars. It is found that certain parameters are important for some isotopes. Future prospects are then briefly discussed.

We study charged rotating black hole solutions of various supergravity theories, both ungauged and gauged, focusing on spacetime dimensions <i>D</i> = 4,5,6,7. These solutions may carry several independent angular momenta and U(1) charges, the precise number depending on the theory. We find asymptotically anti-de Sitter black holes in six-and seven-dimensional gauged supergravity. The six-dimensional solution has two independent angular momenta and one U(1) charge from an SU(2) gauge group. The seven-dimensional solution has three independent angular momenta and two equal U(1) charges from an SO(5) gauge group. We study the thermodynamics of the solutions. These solutions include supersymmetric solutions, amongst which are supersymmetric black holes without naked closed timelike curves. We study the hidden symmetries of the metrics involved. To further illustrate the context of these symmetries, we construct a higher-dimensional charged Kerr solution with NUT parameters. In all cases, we find Killing-Stäckel tensors for a conformally related Jordan-frame metric. These satisfy the conditions for a separability structure and induce conformal Killing-Stäckel tensors for the Einstein-frame metric. We directly verify the separation of the null Hamilton-Jacobi and massless Klein-Gordon equations for some of these solutions.  Simple choices of vielbeins are seen to correspond to eigenforms of privileged Killing-Stäckel tensors of the conformally related metric.

Using quasar absorption lines as a probe of the high redshift universe is a powerful tool in the field of chemical evolution. In this thesis, I consider the elemental abundances in absorbers that correspond to a variety of environments, ranging from high redshift galaxies to the low density intergalactic medium. I firstly address the question of abundances in intermediate redshift (<I>z<SUB>abs</SUB></I> < 1.5) damped Lyα systems (DLAs), objects believed to correspond to the progenitors of present day massive galaxies. I present Hubble Space Telescope (HST) spectra of six intermediate redshift DLAs which have been supplemented with high resolution spectroscopy obtained with the high resolution echelle spectrograph (HIRES) on the Keck telescope. The chemical abundances of a range of elements are investigated and compared with local Galactic values in order to gain an insight into the metallicities, dust-to-gas ratios and star formation histories of these systems. The results from this work have inspired a new survey for DLAs based on a radio-selected sample of QSOs. The motivation for this endeavour has been to determine the extent to which our current view of distant galaxies is obscured by dust. I present intermediate resolution spectra obtained at the Anglo-Australian Telescope (AAT) from which DLAs may be identified. The number statistics of the newly discovered DLAs are analysed in order to determine whether obscuration by dust of background QSOs causes a significant observational bias. Finally, I consider the metallicity of the IGM by studying C IV systems associated with the Lyα forest at <I>z</I> ~ 3. The extent to which the IGM has been polluted with metals will provide important clues to the enrichment mechanism. I firstly investigate the column density distribution function of strong C IV absorbers associated with high column density Lyα clouds. This work is then extended to consider the C IV/H 1 ratio in low column density absorbers which are associated with physically less dense material. The spectra of two high redshift QSOs are analysed using two different techniques, both of which are critically assessed using synthetic spectra.

The detection of high-redshift clusters of galaxies is important in under-standing the evolution of our Universe. Computer simulations, assuming hierarchical structure formation within a Ω_λ » 0.7, Ω<i>_M</i> » 0.3 universe, predict the galaxy clusters should be detected out to redshifts of z = 1. Traditional methods for finding clusters of galaxies, for example using optical plates, are not well to cluster detection beyond a redshift of z = 0.3, because they suffer from contamination of foreground sources. A new method of searching for galaxy clusters has been devised. It uses the hypothesis that at high redshifts radiosources trace high-density regions of our Universe. This would imply that high-redshift groupings of radiosources would be preferentially found in the high-density environments of galaxy clusters. I have used the Sydney University Molonglo Sky Survey (SUMSS) to search for groupings of five radiosources within a seven-arcminute circle. In this thesis I present the work extracting 60 cluster candidates from SUMSS. I also present the radio, infrared and optical follow-up observations that were undertaken and the implications of these. This thesis also discusses the Sunyaev Zel’dovich Effect (SZE), which is the inverse-Compton scattering of the Cosmic Microwave Background (CMB) by a plasma. This is another new method for detecting high-redshift clusters of galaxies. It is particularly important because the magnitude of the effect is independent of redshift. I include the observations of a galaxy cluster where this effect is apparent carried out at the Ryle Telescope (RT) in Cambridge.