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

Accepted..., Received..., in original form.... Properties of ∼ 6 000 Ly-α absorbers observed in 19 high resolution spectra of QSOs are investigated using the model of formation and evolution of DM structure elements based on the Zel’dovich theory. This model is generally consistent with simulations of absorbers formation, describes reasonably well the Large Scale Structure (LSS) observed in the distribution of galaxies at small redshifts and emphasizes the generic similarity of the LSS and absorbers. It asserts that absorbers are formed in the course of both linear and nonlinear adiabatic or shock compression of dark matter (DM) and gaseous matter. It allows us to link the column density and overdensity of DM and gaseous components with the observed column density of neutral hydrogen, redshifts and Doppler parameters of absorbers and demonstrates that at high redshifts we observe a self similar period of structure evolution with the Gaussian initial perturbations. We show that the colder absorbers are associated with rapidly expanded regions of a galactic scale which represent large amplitude negative density perturbations.

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