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Abstract The spectra of high-redshift ( z ≳ 6) quasars contain valuable information on the progression of the Epoch of Reionization. At redshifts z 7 the observed quasar damping wings indicate high neutral gas fractions. However, there remains a gap in neutral gas fraction constraints at 6 ≲ z ≲ 7 where the Lyman-series forest becomes saturated but damping wings have yet to fully emerge. In this work, we use a sample of 18 quasar spectra at redshifts 6.0 x ¯ HI , while jointly fitting for the mean quasar lifetime, t Q , for each stacked spectrum. We chronicle the evolution of neutral gas fraction using the ATON (CROC) models as follows: x ¯ HI = 0.21 − 0.07 + 0.17 ( x ¯ HI = 0.10 10 − 4 + 0.73 ) at 〈 z 〉 = 6.10, x ¯ HI = 0.21 − 0.07 + 0.33 ( x ¯ HI = 0.57 − 0.47 + 0.26 ) at 〈 z 〉 = 6.46, and x ¯ HI = 0.37 − 0.17 + 0.17 ( x ¯ HI = 0.57 − 0.21 + 0.26 ) at 〈 z 〉 = 6.87. At the same time, we constrain the average quasar lifetime to be t Q ≲ 7 Myr across all redshift bins, in good agreement with previous studies.
Ďurovčíková et al. (Mon,) studied this question.