标题： 用金属吸收线探测黑暗时代 显示英文标题

标题： Probing the Dark Ages with Metal Absorption Lines

摘要： 最近对红移约为6的高红移类星体的观测终于揭示了完整的Gunn-Peterson吸收。 然而，这最多只能将体积加权和质量加权的氢中性分数限制为大于10^-3和10^-2；由于氢Lyman跃迁的高光学深度，无法获得更强的限制。 在这里，我建议某些金属线作为氢中性分数的示踪剂。 如果介质被污染到金属丰度Z ~ 10^-3.5--10^-2.5 Z_solar，这些线在电离气体介质几乎完全中性时应产生未饱和吸收。 除非类星体而不是恒星是电离光子的主要来源，否则在再电离的中后期阶段，这种最低水平的金属污染是不可避免的。 1302埃的OI线特别有希望：OI和H的电离势几乎相同，OI应与H处于非常紧密的电荷交换平衡中。SiII 1260埃跃迁也可能可观测。 在高红移下，致密区域首先被污染到高金属丰度，但由于复合时间短，它们最后才会永久电离。 这样的区域应产生波动的OI和SiII森林，如果被观测到，将表明存在大量中性氢。 OI森林可能已经在SDSS z=6.28类星体中可检测到。 如果在未来高红移类星体中看到OI和SiII森林，它们将探测早期宇宙再电离和金属污染的拓扑结构。 如果此外还能从高红移伽马射线暴的阻尼翼测量HI光学深度，它们将提供一个非常可靠的高度红移宇宙金属丰度测量。 显示英文摘要

摘要： Recent observations of high redshift quasars at z~6 have finally revealed complete Gunn-Peterson absorption. However, this at best constrains the volume-weighted and mass-weighted hydrogen neutral fractions to be greater than 10^-3 and 10^-2 respectively; stronger constraints are not possible due to the high optical depth for hydrogen Lyman transitions. Here I suggest certain metal lines as tracers of the hydrogen neutral fraction. These lines should cause unsaturated absorption when the IGM is almost fully neutral, if it is polluted to metallicities Z ~ 10^-3.5--10^-2.5 Z_solar. Such a minimal level of metal pollution is inevitable in the middle to late stages of reionization unless quasars rather than stars are the dominant source of ionizing photons. The OI line at 1302 Angstroms is particularly promising: the OI and H ionization potentials are almost identical, and OI should be in very tight charge exchange equilibrium with H. The SiII 1260 Angstrom transition might also be observable. At high redshift, overdense regions are the first to be polluted to high metallicity but the last to remain permanently ionized, due to the short recombination times. Such regions should produce a fluctuating OI and SiII forest which, if observed, would indicate large quantities of neutral hydrogen. The OI forest may already be detectable in the SDSS z=6.28 quasar. If seen in future high-redshift quasars, the OI and SiII forests will probe the topology of reionization and metal pollution in the early universe. If in additional the HI optical depth can be measured from the damping wing of a high-redshift gamma-ray burst, they will yield a very robust measure of the metallicity of the high-redshift universe.