The Formation of Galaxies from Gas

星系是如何形成的？研究表明，类星体（qso）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，产生这些吸收谱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，富含金属的气体一定位于我们和qso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。这个项目旨在补充传统的星系形成研究，在传统的研究中，重点更多地放在星系早期合并或聚集过程中恒星的形成和命运上。在过去的十年中，宇宙学流体力学计算机模拟表明，大多数星系形成的早期阶段（特别是“暗”星系，在恒星开始发光之前）可以使用它们在背景qso光谱中形成的吸收线来观察。这些谱线的速度结构显示了气体和原星系碎片的流入，来自星系间介质扰动的扭转，以及恒星对气体的反馈和高红移星际介质本身的气体动力学。这个项目的目的是利用观测到的这些低密度、高电离吸收谱线的特性来理解星系和高红移时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）将在最先进的宇宙流体动力学模拟的帮助下进行解释。金属谱线在大尺度上的聚类特性将用于追踪密度远低于明亮高红移源（如射电星系、qso、Lyman-break星系）探测密度的高红移大尺度结构。将检查吸收谱线的轮廓，以确定气体的运动学，并试图确定各种金属吸收谱线所揭示的气相的精确起源，并直接观察物质流入形成星系的过程。在非常接近透镜qso的多个视线中观察吸收系统将有助于量化年轻星系潜在井附近富含金属的气体的密度和速度结构。对气体湍流的测量将决定在多大程度上，星系间介质中令人惊讶的广泛的金属富集是一个最近的过程，还是一个古老的星族III恒星形成阶段的结果。本项目由美国国家科学基金会星系外天文学和宇宙学项目（AST/EXC）资助

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).***