During reionization, neutral hydrogen in the intergalactic medium (IGM) imprints a damping wing absorption feature on the spectrum of high-redshift quasars. A detection of this signature provides compelling evidence for a significantly neutral universe, and enables measurements of the hydrogen neutral fraction x H i (z) at that epoch. Obtaining reliable quantitative constraints from this technique, however, is challenging due to stochasticity induced by the patchy inside-out topology of reionization, degeneracies with quasar lifetime, and the unknown unabsorbed quasar spectrum close to rest-frame Lyα. We combine a large-volume semi-numerical simulation of reionization topology with 1D radiative transfer through high-resolution hydrodynamical simulations of the high-redshift universe to construct models of quasar transmission spectra during reionization. Our state-of-the-art approach captures the distribution of damping wing strengths in biased quasar halos that should have reionized earlier, as well as the erosion of neutral gas in the quasar environment caused by its own ionizing radiation. Combining this detailed model with our new technique for predicting the quasar continuum and its associated uncertainty, we introduce a Bayesian statistical method to jointly constrain the neutral fraction of the universe and the quasar lifetime from individual quasar spectra. We apply this methodology to the spectra of the two quasars with the highest redshifts known, ULAS J1120+0641 and ULAS J1342+0928, and measure volume-averaged neutral fractions and (posterior medians and 68% credible intervals) when marginalized over quasar lifetimes of 103?≤?t q?≤?108 yr.
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机译：在离子化过程中，星系间介质（IGM）中的中性氢在高红移类星体的光谱上具有阻尼机翼吸收特征。对这一特征的检测为明显中性的宇宙提供了令人信服的证据，并能够测量那个时期的氢中性分数x H i（z）。然而，由于电离的由内而外的不规则拓扑所引起的随机性，具有类星体寿命的简并性以及接近静止帧Lyα的未知的未吸收类星体光谱，因此从该技术中获得可靠的定量约束是一项挑战。我们通过对高红移宇宙的高分辨率水动力模拟，将电离拓扑结构的大量半数值模拟与一维辐射传递结合起来，以构建电离期间类星体透射谱的模型。我们采用最先进的方法来捕获偏航类星体晕圈中的阻尼机翼强度分布，而该类星体光晕本应早已离子化，以及其自身的电离辐射在类星体环境中对中性气体的侵蚀。将该详细模型与我们用于预测类星体连续性及其相关不确定性的新技术相结合，我们引入了贝叶斯统计方法，以联合约束各个类星体谱中的宇宙中性部分和类星体寿命。我们将此方法应用于已知的具有最高红移的两个类星体的光谱，即ULAS J1120 + 0641和ULAS J1342 + 0928，并测量体积平均中性分数和（后中位数和68％可信区间）在类星体寿命中被边缘化时103≤≤tq≤≤108年。
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