Hydrodynamical simulations of the Ly alpha forest: Model comparisons

Ne investigate the properties of the Ly alpha forest as predicted by numeri cal simulations for a range of currently viable cosmological models. This i s done in order to understand the dependencies of the forest on cosmologica l parameters. Focusing on the redshift range from 2 to 4, we show that (1) most of the evolution in the distributions of optical depth, flux, and colu mn density can be understood by simple scaling relations; (2) the shape of optical depth distribution is a sensitive probe of the amplitude of density fluctuations on scales of a few hundred kpc; and (3) the mean of the b dis tribution (a measure of the width of the absorption lines) is also very sen sitive to fluctuations on these scales and decreases as they increase. We p erform a preliminary comparison to observations, where available. A number of other properties are also examined, including the evolution in the numbe r of lines, the two-point flux distribution, and the He II opacity.