In this thesis we make a new measurement of the primordial deuterium abundance, and analyse five other systems selected as possible D/H candidates. We also undertake an investigation of systematic errors in a system where an existing deuterium measurement has been made. We measure the number of hydrogen components and their velocity distributions in a moderate and high redshift sample of Lyman limit systems in one Angstrom resolution spectra. We present a new measurement of the deuterium-to-hydrogen ratio, D/H, at z=3.2560 in a newly-discovered low metallicity absorption system towards the quasar PG1937-1009. We attempt to account for any systematic effects that could influence the D/H measurement. We find a 1 sigma range for D/H*1e5 of 1.6 (+0.25) (-0.30). Using high resolution spectra from the Hubble Space Telescope and the Very Large Telescope, we assess the suitability of five D/H candidate absorption systems. These systems were selected as candidates using lower resolution spectra. We measure the neutral hydrogen column density, identify metal lines and analyse the velocity structure of each system, and show them to be unsuitable for measuring D/H. We also investigate the systematic errors in the absorber at z=0.701 towards quasar PG1718-4801 that was initially thought to show a high primordial D/H value. We analyse the dependence of the putative deuterium line's parameters on wavelength calibration errors in the HST spectra and present a revised deuterium measurement. We examine the velocity widths of two samples of one Angstrom resolution quasar spectra showing Lyman limit absorption systems. The first sample is at high redshifts, taken from the Sloan quasar data release 3 catalogue. The second is at intermediate redshifts, compiled from a survey for UV quasar absorption systems taken with the Hubble Space Telescope. We use a modified version of the Voigt profile fitting program, VPFIT, to estimate the number of hydrogen velocity components and column density in the Lyman limit systems. We compare the velocity distributions of the higher and lower redshift samples. We find the distributions are consistent with other measures of the velocity spread in absorption systems, and find no compelling evidence for evolution between the redshift samples.
| Identifer | oai:union.ndltd.org:ADTP/215587 |
| Date | January 2006 |
| Creators | Crighton, Neil, Physics, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. Physics |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Neil Hugh Mackinnon Crighton, http://unsworks.unsw.edu.au/copyright |
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