Statistical characteristics of the observed Ly α forest and the shape of initial power spectrum

• Published in: Monthly notices of the Royal Astronomical Society 2003-04, Vol.340 (2), p.525-542
• Main Authors: Demiański, M., Doroshkevich, A. G., Turchaninov, V.
• Format: Article
• Language: English
• Subjects: large-scale structure of the Universe; quasars: absorption lines
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1046/j.1365-8711.2003.06328.x

Properties of approximately 4500 observed Ly α absorbers are investigated using the model of formation and evolution of dark matter (DM) structure elements based on the modified Zel'dovich theory. This model is generally consistent with simulations of absorber formation, describes the large-scale structure (LSS) observed in the galaxy distribution at small redshifts reasonably well and emphasizes the generic similarity of the LSS and absorbers. The simple physical model of absorbers asserts that they are composed of DM and gaseous matter. It allows us to estimate the column density and overdensity of DM and gaseous components and the entropy of the gas trapped within the DM potential wells. The parameters of the DM component are found to be consistent with theoretical expectations for the Gaussian initial perturbations with the warm dark matter-like power spectrum. The basic physical factors responsible for the evolution of the absorbers are discussed. The analysis of redshift distribution of absorbers confirms the self-consistency of the adopted physical model, Gaussianity of the initial perturbations and allows one to estimate the shape of the initial power spectrum at small scales that, in turn, restricts the mass of the dominant fraction of DM particles to MDM≥ 1.5–5 keV. Our results indicate a possible redshift variations of intensity of the ultraviolet background by approximately a factor of 2–3 at redshifts z∼ 2–3.