Browsing by Author "Fairall, Anthony Patrick"

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    Aspects of modern cosmology
    (1997) Bassett, Bruce Adrian Charles; Ellis, George F R; Fairall, Anthony Patrick
    The main work of this thesis can be summarised as: ■ An implementation of canonical quantisation to the covariant and gauge-invariant approach to cosmological perturbations. Standard results are reproduced. We discuss the advantages of this formalism over non-covariant and non gauge-invariant formalisms. ■ A characterisation of linear gravitational waves in a covariant way is achieved. The evolution equations for the electric and magnetic parts of the Weyl tensor are shown to be of different order. In particular, the electric part appears to have a third order evolution equation, while the magnetic part has a second order evolution equation. It is shown that the "silent" nature of the evolution equations for irrotational dust can be extended to the case of vortical dust. This may be relevant for the endpoints of gravitational collapse since the vorticity begins to grow as soon as density contrast becomes non-linear, as is the case in galaxies, showing that the irrotational silent universes are unstable. The main problem in accepting such vortical silent universes lies in proving integrability of the equations which has not been achieved so far, even in the irrotational case. ■ A review of issues in the Cosmic Microwave Background (CMB) is given, focussing particularly on points such as ergodicity, decaying modes, foreground contamination, recombination, spectral distortions and polarisation of the CMB. ■ A review of methods in gravitational lensing is presented, together with a hierarchy of distance measures in cosmology, forming an introduction to the following two chapters. ■ A common belief that photon conservation implies that the all-sky averaged area distance in inhomogeneous universes must be that of the background, matter-averaged Robertson-Walker area distance is dis proven. This means that there will in general be gravitational lensing effects even on large angular scales. ■ The realistic situation in which gravitational lensing leads to caustic formation is discussed. It is claimed that this invalidates many accepted beliefs concerning high-redshift observations in inhomogeneous universes. One application of importance is the CMB. Possible implications are discussed. ■ Random Gaussian fields are ubiquitous in modern statistical physics, and particularly important in CMB studies. Here we give accurate analytical functions approximating ∫e⁻ˣ²dx, the simplest of which is just the kink soliton.
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    The measurement and analysis of flux variations in Seyfert galaxy nuclei
    (1990) Winkler, Hartmut; Fairall, Anthony Patrick
    Seyfert galaxies have compact nuclei with luminosities only surpassed by quasars, to which they are believed to be related. The most common interpretation of these objects is that their central power source is a black hole with matter accreting towards it. An understanding of these powerful energy sources would vastly increase our knowledge of high energy physics and cosmology. One unexplained characteristic of Seyfert nuclei is that their luminosities are often variable. Some questions relating to this fact are: What is the nature of the variability? How much obscuration is there from matter in the line of sight? What is the shape of the flux continuum? What is the relationship between the variability and other properties of the galaxy and nucleus? This thesis seeks to answer some of these questions, as they critically affect any model put forward to explain the Seyfert phenomenon. 29 southern Seyfert galaxies were chosen for observation. Flux measurements through five colour filters in the 0.3 to 1 μm range were made regularly in the period September 1986 to October 1989 with a single channel photometer and a CCD camera. These were analysed in conjunction with similar data collected by other investigators. Flux changes of 10% or more were observed in most objects. Fluxes through individual colour filters varied proportionally to each other, indicating that the shape of the continuum at these wavelengths remains constant. The flux distribution derived in this manner is shown to be similar for all objects examined. A procedure potentially superior to existing methods is developed to estimate the extinction of Seyfert nuclei from the flux distribution. Spectroscopic observations in the 0.34-0.72 μm range were made for most objects. From these spectra the gas densities and temperatures, degrees of activity and spectral line intensities and widths were derived. Possible spectral variations were investigated. No definite periodic changes in the light curves could be found. However the possibility of regular variations is not completely excluded. The relative amplitude and rate of flux variations are shown to be independent of the luminosity and other nuclear properties.
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    The morphology and absolute diameters of galaxies
    (1980) Block, David Lazar; Fairall, Anthony Patrick
    This is the first time to the author's knowledge that a catalogue of galaxy photographs has been prepared on a uniform physical scale. Of the many interesting aspects which result from such an investigation, we mention here the fundamentally new appreciation both of the diversity of spiral arm texture, and in the range of the intrinsic diameters of galaxies, particularly the spirals. Small, high surface brightness spiral galaxies form an important subgroup; these present a saturated or predominantly saturated image on the SRC IIIa-J Survey. An intercomparison of their appearance on the J-film copies and those of the "Quick Blue" Survey shows an inner morphology often indicative of substantial differential rotation effects. One of our galaxies in the sample shows significant signs of warping; the spiral has no bright, close companions. Also of note are faint, featureless outer envelopes in some of the spirals, and galaxies with faint outer spiral arms whose pitch angles are significantly different from those of the central inner region. Further results are discussed in chapter 3 onwards. A by-product of this investigation is the identification of the largest known (type b) barred spiral.
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    Photometry of elliptical galaxies in crowded starfields
    (2006) Markus, Karsten; Fairall, Anthony Patrick; Woudt, Patrick Alan
    Includes bibliographical references.
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    Probing distant clusters : a pre-SALT photometric study of intermediate redshift galaxy cluster
    (2005) Cluver, Michelle E; Fairall, Anthony Patrick; Woudt, Patrick Alan
    Includes bibliographical references (p. 273-279).
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    Southern voids : structure and cosmological implications
    (1997) Andersson, Yuri Luis Escutia; Fairall, Anthony Patrick
    A review of standard cosmology theory and observational results is presented. The main tool for investigating large-scale structure in this thesis is a visually compiled void catalogue. Void selection effects that cause the detected distribution of voids to differ from the true distribution are discussed and suggestions are made for how to correct for these effects in the catalogue. The geometrical distribution of voids is then studied by dividing the void catalogue into two parts - wall voids and non-wall voids. The wall voids are smaller with typical radii of around 150 km s-¹ whereas non-wall voids have a mean radius of approximately 1150 km s-¹. The non-wall, and therefore, the larger voids are distributed isotropically and their correlation function is found to correspond roughly to that of Abell clusters, thus suggesting a link between the two structures. A relation between the velocity dispersions of clusters and the void radii is found using a spherical collapse model for structure formation. The ratio of these two quantities is used to put constraints on the cosmic density parameter 0 and observational data indicate that the universe is open.
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    Voids in the distribution of galaxies : an assessment of their significance and implications for large-scale structure formation theories
    (1990) Kauffmann, Guinevere; Fairall, Anthony Patrick
    Chapter I gives an overview of the current well-known theoretical models of large-scale structure formation and explains how the predictions of these models can be tested by the investigation of voids in the distribution of galaxies. Chapter II reviews work that has already been done on the statistics and properties of voids. In particular, attention is focussed on the establishment of a new statistic, the void probability function, which is sensitive to the presence of voids and is intimately linked to the hierarchy of N-point correlation functions derived by Peebles (1980). Chapter II also contains a brief review of the work done by Gott on point-smoothing analysis and the use of the topological genus parameter to distinguish between various theoretical models of structure formation. Chapters III and IV present the original work done by the author in establishing a method of · surveying all important voids in the available data. A systematic search for all voids out to a redshift of about 15000 km/s is described. Methods of assessing the significance of these voids are discussed. Upon applying these methods, a list of "statistically significant" voids is constructed and this list is used to derive a spectrum of void sizes. Finally, these chapters illustrate how this new technique of studying voids might serve as an important tool in determining the origins of the large-scale structure observed in the universe today.