Reionization bias in high-redshift quasar near-zones

Abstract

Absorption spectra of high-redshift quasars exhibit an increasingly thick Lyα forest, suggesting that the fraction of neutral hydrogen in the intergalactic medium (IGM) is increasing towards z ∼ 6. However, the interpretation of these spectra is complicated by the fact that the Lyα optical depth is already large for neutral hydrogen fractions in excess of 10-4, and also because quasars are expected to reside in dense regions of the IGM. We present a model for the evolution of the ionization state of the IGM which is applicable to the dense, biased regions around high-redshift quasars as well as more typical regions in the IGM. We employ a cold dark matter based model in which the ionizing ph..