Low-redshift quasar absorption-line systems: inside and around galaxies

We present semi-analytic models and monte-carlo simulations of QSO Lyα absorption line systems which originate in gaseous galactic halos, galaxy disks, and satellite halos around central galaxies. The relation between the properties of predicted absorption lines and those of galaxies has been investigated. Using a model with galactic halos, satellites, and hi disks of spirals, 60 % of the observed strong Lyα lines and all of the Lyman-limit systems can be predicted. The models predict w_r ∝ ρ^-α l_b^β (1+z)^-γ with α ∼ 0.5, β ∼ 0.15, γ ∼ 0.5. For strong Lyα lines the average covering factor within 250 h^-1 kpc is ∼ 0.36, with an average absorption radius of ∼ 150 h^-1 kpc for a galaxy halo, in good agreement with observations. Using mock imaging and spectroscopic surveys, selection effects are found to be able to strengthen the anti-correlation between line width and projected distance. The models were also applied to quasar metal absorption lines and more realistic absorption spectra with noise were simulated.