Did the universe reionize at redshift six?

In light of recent observations of spectra of the quasars SDSS 1030+0524 [J. Becker et al., AJ (2001), submitted] and SDSS 1044-0125 (Djorgovski et al., 2001), we study the observational signatures of different stages of the reionization epoch. During the initial pre-overlap stage, the hydrogen throughout the universe is neutral except for isolated H II bubbles due to individual ionizing sources. The central stage of reionization is the overlap stage, during which the individual H II bubbles overlap each other and reionize the low-density gas which takes up most of the volume of the universe. Some neutral hydrogen remains in dense clumps which are then slowly reionized during post-overlap. We show that both of the recent observations are consistent with the post-overlap stage. Becker et al. [AJ (2001), submitted] may have observed the universe in the era before the end of overlap, but a conclusive proof of this requires the observation of similar intervals of Gunn-Peterson absorption at the same redshift along several additional lines of sight. (C) 2002 Published by Elsevier Science B. V.