Heavy Element Abundances at High Redshifts

在过去的几年里，我们在理解星系间介质的起源和性质方面取得了显著的进展，这种介质在遥远的类星体的光谱中产生了被称为“莱曼-阿尔法森林”的吸收特征。研究表明，莱曼-阿尔法森林是以丝状和片状排列的扩展电离气体的观测特征，被称为宇宙网，星系从宇宙网中凝聚。因此，莱曼-阿尔法吸收的观测不仅探测宇宙的电离历史和重子密度，而且还探测导致结构形成的暗物质变化。这个项目将a)确定负责电离星系间气体的辐射的强度和来源，b)使用高分辨率光谱来研究再电离时代结束时的星系间云，c)发现更多在银河系外流中产生的特殊类型的吸收体，以及d)确定星系间空间最稀薄区域的重元素组成。这项工作将对物质大规模分布的观测与理论家进行的数值模拟相结合。有足够的大型望远镜可以获取这些尚未掌握的数据。这位首席研究员与英国、日本、荷兰和澳大利亚的科学家合作，他收集的数据被美国各地以及波兰、俄罗斯、荷兰和英国的同事使用。这些数据还被用于其他科学领域，特别是用于调查地球大气的组成及其季节性和长期变化。因此，这项工作除了通过出版物和相关的学生培训产生影响外，还具有广泛的影响。

AST-0606868SargentThe past few years have witnessed remarkable progress in our understanding of the origin and properties of the intergalactic medium, which gives rise to the absorption features known as the "Lyman-alpha forest", in the spectra of distant quasars. Studies have shown that the Lyman-alpha forest is the observational signature of an extended ionized gas arranged in the shape of filaments and sheets, known as the cosmic web, from which galaxies condense. Thus, observations of Lyman-alpha absorption probe not only the ionization history and baryon density of the Universe, but also the dark matter variations that lead to the formation of structure. This project will a) determine the intensity and source of the radiation responsible for ionizing the intergalactic gas, b) use high resolution spectra to investigate inter-galactic clouds at the end of the reionization era, c) find more of a special class of absorbers produced in galactic outflows, and d) determine the heavy element composition of the most tenuous regions of intergalactic space. The work unites observations of the large-scale distribution of matter with numerical simulations carried out by theorists. There is sufficient large telescope access to obtain those data not already in hand.This Principal Investigator collaborates with scientists in Great Britain, Japan, Holland and Australia, and his collected data are used by colleagues across the US as well as in Poland, Russia, Holland and Great Britain. These data are also used in other fields of science, notably to investigate the composition of the earth's atmosphere and its seasonal and long-term changes. This work thus has a widespread impact in addition to its influence through publications and the associated student training.