Self‐Absorption of Ionizing Radiation and Extended Narrow‐Line Emission in High‐Redshift Quasi‐stellar Objects

Abstract

We calculate the H I column density of self-absorption in quasi-stellar objects (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 beyond the photoionization effect. When clumping of the gas is ignored, the derived H I column densities produce negligible Lyman limit absorption even in the lowest luminosity QSOs with an optical depth of ~10% for luminosity L = 0.01LB* when P0 = 10-2. We also compute the He II Lyman limit self-absorption, which is slightly higher but still small. The self-absorption is increased if the gas is highly clumped; for P0 = 10-2, a clumping factor of ~10 results in a significantly reduced overall emissivity of H I Lyman limit photons from QSOs and affects the predicted intensity of the ionizing background. A clumping factor of ~5 is sufficient to reduce the He II Lyman limit emissivity and to delay the predicted epoch of He II reionization. The presence of the gas associated with damped absorption systems around QSOs can also be detected from the narrow Lyα emission line, which should have an angular extent of 01-1'' in typical high-redshift QSOs.