标题： 星际和星系际的未见 $z=6.84$ 星系的特性：最早已知类星体吸收体中的丰度、电离和加热 显示英文标题

标题： Interstellar and Circumgalactic Properties of an Unseen $z=6.84$ Galaxy: Abundances, Ionization, and Heating in the Earliest Known Quasar Absorber

摘要： 我们分析了一个在红移z=6.84处观测到的强吸收系统中的相对丰度和电离条件，该系统出现在红移z=7.54背景类星体ULAS J134208.10+092838.61的光谱中。 单电离的C、Si、Fe、Mg和Al的测量结果与一个金属贫乏但并非化学原始的温暖中性介质一致。 C IV和Si IV的确定性非检测表明，任何IGM或CGM的温暖电离相尚未超过超金属贫乏范围（<0.001Z_{太阳能}），这与较低红移DLAs中这些线几乎无处不在的情况不同。 重元素的相对丰度在大爆炸后794 Myr时与中等红移的金属贫乏damped Lyman Alpha系统以及银河系晕星相似，并未显示出增强的[alpha/Fe]、[C/Fe]或其他由大质量恒星产量主导的特征。 对CII*精细结构线的检测揭示了局部激发源，这些激发源来自加热，超过了宇宙微波背景提供的光致激发水平。 我们估计了总冷却率和[CII]冷却率，与星际介质加热源平衡，从而发展了一个关于中性介质的经验两相模型。 所暗示的加热需要恒星形成表面密度略高于银河系，但并未达到强烈恒星爆发的水平。 对于典型的（假设的）NHI=10^{20.6}，[Fe/H]=-2.2与中性相中各物种的柱密度相符。 为了在C IV中不被检测到，温暖电离相要么需要在1 kpc的吸收路径上具有非常低的[C/H]<-4.2，要么需要非常小的吸收路径（几pc）。 尽管仍属推测，这些结果表明在星际介质的中性恒星形成区域之外，重元素的富集显著减少，这符合银河系化学演化早期阶段的预期。 显示英文摘要

摘要： We analyze relative abundances and ionization conditions in a strong absorption system at z=6.84, seen in the spectrum of the z=7.54 background quasar ULAS J134208.10+092838.61. Singly ionized C, Si, Fe, Mg, and Al measurements are consistent with a warm neutral medium that is metal-poor but not chemically pristine. Firm non-detections of C IV and Si IV imply that any warm ionized phase of the IGM or CGM has not yet been enriched past the ultra-metal-poor regime (<0.001Z_{solar}), unlike lower redshift DLAs where these lines are nearly ubiquitous. Relative abundances of the heavy elements 794 Myr after the Big Bang resemble those of metal-poor damped Lyman Alpha systems at intermediate redshift and Milky Way halo stars, and show no evidence of enhanced [alpha/Fe], [C/Fe] or other signatures of yields dominated by massive stars. A detection of the CII* fine structure line reveals local sources of excitation from heating, beyond the level of photo-excitation supplied by the CMB. We estimate the total and [CII] cooling rates, balancing against ISM heating sources to develop an heuristic two-phase model of the neutral medium. The implied heating requires a surface density of star formation slightly exceeding that of the Milky Way but not at the level of a strong starburst. For a typical (assumed) NHI=10^{20.6}, an abundance of [Fe/H]=-2.2 matches the columns of species in the neutral phase. To remain undetected in C IV, a warm ionized phase would either need much lower [C/H]<-4.2 over an absorption path of 1 kpc, or else a very small absorption path (a few pc). While still speculative, these results suggest a significant reduction in heavy element enrichment outside of neutral star forming regions of the ISM, as would be expected in early stages of galactic chemical evolution.