The Formation of Galaxies from Gas

星系是如何形成的？研究表明，类星体的光谱中有许多来自比氦重的元素的高红移吸收线。目前的大多数理论表明，产生这些吸收线的化学元素一定是在大爆炸后形成的恒星（所谓的Pop III星）中产生的。然而，当在类星体光谱中观察时，这些吸收线表明富含金属的气体必须位于位于我们和类星体之间的云中。这个项目的目标是试图了解这种气体在早期宇宙中星系形成中的作用，在高红移。该计划旨在补充传统的星系形成研究，其中重点更多地放在早期合并或集群过程中星系中恒星的形成和命运上。在过去的十年中，宇宙学流体动力学计算机模拟表明，大多数星系形成的早期阶段（特别是在恒星开始发光之前的“暗”阶段）可以使用它们在背景类星体光谱中形成的吸收线来观察。这些线的速度结构显示了气体和原星系碎片的下落，来自星系际介质中扰动的转向，以及恒星反馈到气体中和高红移星际介质本身的气体动力学。这个程序的目的是利用这些低密度的观测特性，高电离吸收线，以了解在高红移星系和气体流入和流出之间的关系。观测到的吸收系统的统计数据（将从几个大型望远镜获得）将在最先进的宇宙学流体动力学模拟的帮助下进行解释。金属线在大尺度上的成团特性将被用来追踪密度远低于明亮的高红移源（如射电星系，类星体，莱曼破裂星系）探测的高红移大尺度结构。将检查吸收线轮廓，以确定气体的运动学，并试图确定各种金属吸收线所揭示的气相的精确起源，并直接观察物质进入形成星系的过程。在非常接近的多个视线透镜类星体的吸收系统的观测将有助于量化的密度和速度结构的年轻星系的潜在威尔斯附近的金属富集气体。对气体湍流的测量将决定星系际介质中令人惊讶的广泛金属富集在多大程度上是一个最近的过程或古老的星族III阶段的恒星形成的结果。该项目的资金由美国国家科学基金会的河外天文宇宙学计划（AST/EXC）提供。

ABSTRACT AST 0098492RauchHow do galaxies form? Studies show that the Quasars (QSOs) have many high redshift absorption lines from elements heavier than Helium in their spectra. Most current theories indicate that the chemical elements which give rise to these absorption lines must have been made in stars formed after the Big Bang (the so called Pop III stars). Yet when observed in quasar spectra, these absorption lines show that the metal enriched gas must be in clouds which lie between us and the QSOs.The goal of this project is to try and understand the role of this gas in galaxy formation in the early universe, at high redshift. This program is designed to complement traditional studies of galaxy formation where the emphasis has been more on the formation and fate of the stars in galaxies during the early merger or clustering process. Over the past decade, cosmological hydrodynamic computer simulations have shown that most of the early stages of galaxy formation (in particular the "dark" ones, before stars started to shine) can be observed using the absorption lines which they form in the spectra of background QSOs. The velocity structure of these lines shows infall of gas and protogalactic fragments, from the turnaround of perturbations in the intergalactic medium, as well as stellar feedback into the gas and the gasdynamics of the high redshift interstellar medium itself.The aim of this program is to use the observed properties of these low density, high ionization absorption lines to understand the relation between galaxies and gaseous inflows and outflows at high redshift. The statistics of the observed absorption systems (to be obtained from several large telescopes) will be interpreted with the help of state-of-the-art cosmological hydrodynamic -simulations. The clustering properties of metal lines on large scales will be used to trace the high redshift large scale structure at densities much lower than those probed by bright high redshift sources (e.g. radio galaxies, QSOs, Lyman-break galaxies). Absorption line profiles will be examined to determine the kinematics of the gas, and attempts will be made to identify the precise origin of the gas phases revealed by various metal absorption lines and to directly observe the infall of matter into forming galaxies. Observations of absorption systems in very close multiple lines of sight to lensed QSOs will help to quantify the density and velocity structure of the metal enriched gas near the potential wells of young galaxies. Measures of the turbulence of the gas will decide to what degree the surprisingly widespread metal enrichment of the intergalactic medium is a recent process or the result of an ancient Population III phase of starformation. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC).***