Cosmology with the Lyman alpha forest
: effects of quasar redshift uncertainties on correlation functions & a novel source for Weak Gravitational Lensing

  • Samantha Jane Youles

Student thesis: Doctoral Thesis


The field of Lyman-alpha (Lyα) forest cosmology is now well-established and over the last few years has become an important cosmological probe. It has been used to measure Baryon Acoustic Oscillations (BAO) at high redshift, providing significant constraints on parameters of ΛCDM , the standard cosmological model. Additionally, it has been used to measure the matter power spectrum at small scales, constraining the mass of neutrinos and models of warm dark matter.
In this thesis, I execute an analysis of the impact of errors in the estimation of quasar redshifts on the Lyα baryon acoustic oscillation parameters, discovering a previously unknown source of systematic error. The nature of the contamination is explained, and a model of the effect is developed. This work will enable the effect to be included in the fit of the correlation functions in the Lyα pipeline for current and future surveys, improving the cosmological constraints from Lyα BAO measurements.
In a separate work, I perform a detailed study of weak gravitational lensing of Lyα forests, using a new quadratic estimator and synthetic data developed for use with the extended Baryon Oscillation Spectroscopic Survey (eBOSS) and Dark Energy Spectroscopic Instrument (DESI). I find that the power of the reconstructed lensing signal is strongly dependent on the density of quasars observed, and that it should be possible to obtain a first detection with the DESI survey within the next five years.
Date of AwardDec 2021
Original languageEnglish
SupervisorJulian Ernesto Bautista (Supervisor), David Bacon (Supervisor) & William James Percival (Supervisor)

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