论文标题
$ z = 6.84 $ Galaxy的星际和周围的特性：最早已知的类星体吸收器中的丰度，电离和加热
Interstellar and Circumgalactic Properties of an Unseen $z=6.84$ Galaxy: Abundances, Ionization, and Heating in the Earliest Known Quasar Absorber
论文作者
论文摘要
我们在z = 6.84处的强吸收系统中分析了相对丰度和电离条件，在z = 7.54背景的quasar ulas j134208.10+092838.61中可见。单一离子化的C，Si，Fe，Mg和Al测量与金属贫困但不是化学原始的温暖中性培养基一致。 C IV和SI IV的牢固的非检测意味着，与较低的Redshift DLA不同，IGM或CGM的任何温暖的IgM或CGM的温暖离子化阶段尚未富集超过超金属贫困状态（<0.001Z_ {solar}），而这些线几乎无处不在。大爆炸后，重元素的相对丰度794 MYR类似于中间红移和银河系中的金属贫困型Lyman Alpha系统的相对丰度，并且没有显示出增强的[Alpha/Fe]，[C/FE]或其他由大型恒星主导的产量的签名的证据。对CII*良好结构线的检测显示，除了CMB提供的光启动水平，加热的局部激发源。我们估计总冷却速率和[CII]冷却速率，与ISM加热源保持平衡，以开发中性培养基的启发式两相模型。隐含的加热需要恒星形成的表面密度略微超过银河系的表面密度，但不超过强烈的星爆。对于典型的（假设）nhi = 10^{20.6}，在中性相中，丰富的[Fe/H] = - 2.2与物种柱匹配。为了在C IV中保持未检测，温暖的离子化相在1 kpc的吸收路径上需要更低的[C/H] <-4.2，或者是非常小的吸收路径（几个PC）。尽管仍然推测，但这些结果表明，正如银河化学演化的早期阶段所预期的那样，ISM中性恒星形成区域之外的重元素富集显着降低。
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.
