2021/03/31 by Shi-Fan Chen, Zvonimir Vlah, Martin White
Physics and Astronomy · #Anisotropy #Astronomy and Astrophysical Research #Cosmological perturbation theory #Electrical and Electromagnetic Research #Galaxies: Formation, Evolution, Phenomena #Isotropy #Observable #Perturbation (astronomy) #Perturbation theory (quantum mechanics) #Primordial fluctuations #Quadratic equation #Spectral density #astro-ph.CO
paper · pdf · doi:10.1088/1475-7516/2021/05/053
28 pages, 4 figures, updated to match version accepted by JCAP
openalex created_date 2021/03/29 · openalex publication_date 2021/05/01 · arxiv created 2021/05/10 · arxiv updated 2021/06/02 · openalex updated_date 2026/08/05
Abstract The Lyα forest provides one of the best means of mapping large-scale structure at high redshift, including our tightest constraint on the distance-redshift relation before cosmic noon. We describe how the large-scale correlations in the Lyα forest can be understood as an expansion in cumulants of the optical depth field, which itself can be related to the density field by a bias expansion. This provides a direct connection between the observable and the statistics of the matter fluctuations which can be computed in a systematic manner. We discuss the way in which complex, small-scale physics enters the predictions, the origin of the much-discussed velocity bias and the `renormalization' of the large-scale bias coefficients. Our calculations are within the context of perturbation theory, but we also make contact with earlier work using the peak-background split. Using the structure of the equations of motion we demonstrate, to all orders in perturbation theory, that the large-scale flux power spectrum becomes the linear spectrum times the square of a quadratic in the cosine of the angle to the line of sight. Unlike the case of galaxies, both the isotropic and anisotropic pieces receive contributions from small-scale physics.