Measuring the Cosmological Constant Through the Lyman -Alpha Forest Using the Alcock -Paczynski Test
Lin, Wen-Ching
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https://hdl.handle.net/2142/85174
Description
Title
Measuring the Cosmological Constant Through the Lyman -Alpha Forest Using the Alcock -Paczynski Test
Author(s)
Lin, Wen-Ching
Issue Date
2003
Doctoral Committee Chair(s)
Michael Norman
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Language
eng
Abstract
An important topic in cosmology is the determination of the energy densities of the major components of the Universe---OB, O DM and OLambda. Among these, the cosmological constant OLambda, which associates with the vacuum energy of our universe, draws specific attentions for its importance in fundamental particle physics. The Lyalpha forest QSO spectra are observationally available from z ∼ 0 to z ∼ 4. Recently the concept of performing the Alcock-Paczynski test on the Lyalpha forest to determine the cosmological constant has been proposed. This motivates us to develop a methodology incorporating sophisticated cosmological hydrodynamics simulations including these effects to implement the AP test and to perform an accurate measurement on the cosmological constant O Lambda. To manipulate the data from paired QSO spectra with different angular separations, we propose an explicit method based on the maximum likelihood estimation. We use this method to implement the AP test and demonstrate the whole procedure based on our numerical simulations. Using mock pair spectra, we estimate that more than 40 pairs are required to derive an accurate value of OLambda due to the impact of cosmic variance. The degeneracy of other cosmological parameters is an important topic for this project. We examine two other parameters, sigma8 and n, the initial power spectrum amplitude and index, whose value are not consistently derived through other means. We conclude that when the uncertainties of these two parameters are around 10%--20%, the resulting bias in O Lambda is less than 10%. Using a small sample of currently available QSO pairs, we have derived OLambda = 0.65+0.39-1.16 . Our preliminary result encourges us to take further steps on this project.
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