Self-Absorption of Ionizing Radiation and Extended Narrow-Line Emission in High-Redshift QSOs

We calculate the neutral hydrogen column density of self-absorption in QSOs predicted in a model where the QSOs are located in the same halos that contain the gas in damped Lyα absorption systems. The model is parameterized by the probability P0 that any halo has an active QSO. We assume that the QSOs ionize the gas, but do not expel or heat it. The derived H I column densities produce negligible Lyman limit absorption, even in the lowest luminosity QSOs, with an optical depth of only ∼ 10% for luminosity L = 0.01L∗, when P0 = 10 . We also compute the He II Lyman limit self-absorption, which is slightly higher but still negligible. The self-absorption can be higher if the gas is highly clumped; only in this case the overall emissivity from QSOs could be significantly reduced due to absorption by the known damped Lyα systems, to affect the predicted intensity of the ionizing background or the epoch of He II reionization. The presence of the gas associated with damped absorption systems around QSOs could also be detected from the narrow Lyα emission line, which should have and angular extent of 0.1 to 1 in typical high-redshift QSOs. Subject headings: intergalactic medium—large-scale structure of universe — quasars: absorption lines Department of Astronomy, The Ohio State University, Columbus, OH 43210; alam,[email protected] Alfred P. Sloan Fellow