Cosmology from the Lyman-alpha forest
Abstract
One of the main goals of research in cosmology is to find and exploit observable properties of the universe which can be computed theoretically and are sensitive to properties of the cosmological model. This thesis discusses one observable: the absorption in quasar spectra by the neutral hydrogen in the intergalactic medium (IGM), called the Lyα forest. I work to establish the Lyα forest as a cosmological probe. Some of the primary results are: (1) The transmitted flux probability distribution function (TFPDF), and the power spectrum and correlation function of the transmitted flux in the Lyα forest are determined from observed quasar spectra, and presented in tabular form to allow for comparisons with theoretical calculations and with other data sets. (2) Excellent agreement is found between the observed TFPDF and the predictions of a numerical simulation of the Lyα forest in a flat CDM model with a cosmological constant and Ω m = 0.4. (3) By a comparison between the measured flux power spectrum and predictions of the same numerical simulation, the amplitude of the mass power spectrum is found to correspond to a linear variance per unit ln k of D2rk = 0.72 ± 0.09 at k = 0.04(km s−1 )−1 and z = 3, and the slope of the power spectrum near the same k to be n p = −2.55 ± 0.10. (4) The redshift evolution of the Lyα forest mean transmitted flux is used to infer the evolution of the intensity of the ionizing background that pervades the IGM. The proper background intensity declines gradually with redshift, decreasing by a factor ∼3 between z = 3 and z = 5. (5) By comparing observed and simulated spectra, the temperature of the IGM at a density 1.4 times the mean is measured to be T1.4 = (20100 ± 2800, 20300 ± 1400, 20700 ± 1900) K at redshift z¯ = (3.9, 3.0, 2.4). (6) A new method is proposed for measuring the cosmological geometry at z ∼ 2 (which is sensitive to the presence of a cosmological constant), using the correlation function of the Lyα forest in multiple lines of sight. (7) Simulation methods are developed to compute the redshift-space anisotropy of the Lyα forest absorption, which must be understood in order to measure the geometry. ^
Subject Area
Physics, Astronomy and Astrophysics
Recommended Citation
Patrick Vincent McDonald,
"Cosmology from the Lyman-alpha forest"
(January 1, 2001).
Dissertations available from ProQuest.
Paper AAI3015344.
http://repository.upenn.edu/dissertations/AAI3015344
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