Measuring the Cosmological Constant Through the Lyman -Alpha Forest Using the Alcock -Paczynski Test

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Astronomy

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Lin, Wen-Ching

Contributors dc:contributor

• Michael Norman

• Physics, Astronomy and Astrophysics

Language dc:language

eng

Identifier

(MiAaPQ)AAI3111570

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/85174