Probing the universe with the Lyman-alpha forest: II. The column density distribution

I apply the well controlled Hydro-PM approximation of Gnedin & Hui to model the column density distribution of the Lyman-alpha forest for 25 different flat cosmological scenarios, including variants of the standard CDM, tilted CDM, CDM with a cosmological constant, and CHDM models. I show that within the accuracy of the HPM approximation the slope of the column density distribution reflects the degree of nonlinearity of the cosmic gas distribution and is a function of the rms linear density fluctuation at the characteristic filtering scale only. The amplitude of the column density distribution, expressed as the value for the ionizing intensity, is derived as a function of the cosmological parameters (to about 40% accuracy). The observational data are currently consistent with the value for the ionizing intensity being constant in the redshift interval z~2-4.Comment: Revised version; submitted to MNRA

Reionization, SLOAN, and WMAP: is the Picture Consistent?

I show that advanced simulations of cosmological reionization are able to fit the observed data on the mean transmitted flux in the hydrogen Lyman-alpha line at z~6. At the same time, posteriori models can be constructed that also produce a large value (20%) for the Thompson scattering optical depth, consistent with the WMAP measurements. Thus, it appears that a consistent picture emerges in which early reionization (as suggested by WMAP) is complete by z~6 in accord with the SLOAN data.Comment: accepted for publication in Ap

Computer Simulations of Cosmic Reionization

The cosmic reionization of hydrogen was the last major phase transition in the evolution of the universe, which drastically changed the ionization and thermal conditions in the cosmic gas. To the best of our knowledge today, this process was driven by the ultra-violet radiation from young, star-forming galaxies and from first quasars. We review the current observational constraints on cosmic reionization, as well as the dominant physical effects that control the ionization of intergalactic gas. We then focus on numerical modeling of this process with computer simulations. Over the past decade, significant progress has been made in solving the radiative transfer of ionizing photons from many sources through the highly inhomogeneous distribution of cosmic gas in the expanding universe. With modern simulations, we have finally converged on a general picture for the reionization process, but many unsolved problems still remain in this young and exciting field of numerical cosmology.Comment: Invited Review to appear on Advanced Science Letters (ASL), Special Issue on Computational Astrophysics, edited by Lucio Maye

Local Group Dwarf Galaxies and the Star Formation Law at High Redshift

I show how the existing observational data on Local Group dwarf galaxies can be used to estimate the average star formation law during the first 3 Gyr of the history of the universe. I find that the observational data are consistent with the orthodox Schmidt law with a star formation efficiency of about 4 percent if the star formation is continuous (during the first 3 Gyr). The efficiency is proportionally higher if most of the gas in the dwarfs was consumed (and never replenished) in a short time interval well before the universe turned 3 Gyr.Comment: accepted for publication in ApJ Letter