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Session 85 - Quasar Absorption Line Systems.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We performed 3-D simulations of Ly\alpha clouds in the standard CDM cosmology with a powerful two-level hierarchical hydrodynamic code with fully coupled non-equilibrium evolution for the following chemical species: H, H^+, He, He^+, He^++, and e^-. The standard spectrum fitting procedure with a careful treatment of line blending is used to extract the statistical properties for the distribution and evolution of Ly\alpha forest lines. We obtained the following major results which agree with observational data, especially the new KECK data: the distribution of column densities follows a single power law with exponent \beta\sim1.5 and shows an apparent deficiency of lines above column density \sim10^15 cm^-2; a Gaussian fit to the Doppler parameter distribution yields a median of \sim25 km s^-1; the Doppler parameters shows a lower cutoff which increases slightly with column density; the distribution of equivalent width can be fitted to an exponential with W\sim0.3 and shows a weak overabundance for W<0.2. The evolution of the number of clouds with redshift is slower than most observations found. We also quantitatively demonstrate that a significant number of lower column density lines originate from underdense regions or mini-voids.
