Collaborative Research: Cosmology with the Lyman Alpha Forest

合作研究：与莱曼阿尔法森林的宇宙学

• 批准号: 0341826
• 负责人: Matias Zaldarriaga
• 金额: $ 5.76万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-04-10 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0341826&HistoricalAwards=false
• 关键词: Collaborative; Research; Cosmology; Lyman; Alpha

ABSTRACT AST 0098506ZaldarriagaThis is a Collaborative Research Project with Lam Hui (0098437) of Columbia University.The light from a quasar (also called a qso) often has multiple dips in intensity, or absorption lines, at positions corresponding to the redshifted Lyman alpha line (at rest wavelength 1216 angstroms) from neutral hydrogen. These often occur as a series of absorption lines, called the Lyman alpha forest. The redshift is caused by the expansion of the universe. If we can calculatehow the universe is expanding (based on a cosmological model), we can tell where the photons were absorbed in relation to us. Thus, we can use the absorption map to plot the positions ofclouds of intervening hydrogen between the quasar and us. The clouds in the Lyman alpha systems are not very massive compared to objects like galaxies. Because of this, reliable computer simulations (numerical experiments) of their gravitational collapse (formation) from primordial fluctuations are possible. These Lyman alpha forest simulations produce structure similar to what we see in the nearby universe (filaments, walls, and voids ) by starting with small fluctuations in matter density and then letting gravity and other known forces act. These detailed calculations of the structure and distribution of matter are at the frontiers of current research and these recent advances in computer modeling have made it possible to use observations of the Lyman-alpha forest at redshifts between 2 and 4 as powerful cosmological tools. The forest has offered, and will continue to offer, interesting constraints on many quantities such as the amplitude and shape of the primordial mass power spectrum, the neutrino mass, the matter density, the cosmological constant, and the reionization epoch. These constraints, in conjunction with those from other observations, provide important checks on our fundamental understanding of cosmology.This project will primarily focus on the "transmission power spectrum", a statistic used in cosmological models which is directly observable. The program has two goals:1) Examination of fundamental assumptions: The project will test several methods to address questions about the influence of continuum-fitting in determining the measured fluctuations in the forest , the interpretation of these fluctuations in terms of mass fluctuations resulting from gravitational instability, and the effect of fluctuations in the ionizing background and the effective equation of state of the intergalactic medium on the interpretation. 2) Maximizing the scientific return from the data: To this end the program will address redshift-distortions, (which affect both the program of mass power spectrum recovery, as well asthe ability to measure the cosmological constant through its geometrical distortion of thecorrelation function), degeneracies among parameters (by performing a full likelihood analysiswhich will reveal the degeneracies in the 4 to 6 free parameters in the current model of the forest), and obtaining a better understanding of the thermal history of the universe, (by using the drop in temperature with time after reionization to infer or at least limit the epoch of reionization from measurements of the temperature using the small-scale cut-off of the transmission powerspectrum at redshifts between 2 and 4.)Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC).***

摘要 AST 0098506Zaldarriaga 这是与哥伦比亚大学 Lam Hui (0098437) 的合作研究项目。来自类星体（也称为 qso）的光通常在与红移的莱曼 α 线相对应的位置处有多个强度或吸收线下降（静止波长 1216 埃）来自中性氢。这些通常以一系列吸收线的形式出现，称为莱曼阿尔法森林。红移是由宇宙膨胀引起的。如果我们可以计算宇宙如何膨胀（基于宇宙学模型），我们就可以知道光子在与我们相关的位置被吸收。因此，我们可以使用吸收图来绘制类星体和我们之间的氢云的位置。与星系等物体相比，莱曼阿尔法系统中的云并不是很大。正因为如此，对它们因原始波动而发生的引力塌缩（形成）进行可靠的计算机模拟（数值实验）是可能的。这些莱曼阿尔法森林模拟通过从物质密度的微小波动开始，然后让重力和其他已知力起作用，产生类似于我们在附近宇宙中看到的结构（细丝、墙壁和空隙）。这些对物质结构和分布的详细计算处于当前研究的前沿，而计算机建模的最新进展使得利用对红移 2 到 4 之间的莱曼阿尔法森林的观测作为强大的宇宙学工具成为可能。森林已经并将继续提供对许多量的有趣约束，例如原始质量功率谱的幅度和形状、中微子质量、物质密度、宇宙常数和再电离纪元。这些约束与其他观测结果相结合，为我们对宇宙学的基本理解提供了重要的检验。该项目将主要关注“传输功率谱”，这是宇宙学模型中使用的一种可直接观测的统计数据。该计划有两个目标：1）检查基本假设：该项目将测试几种方法来解决有关连续拟合在确定森林中测量的波动的影响的问题，以及对这些波动的解释引力不稳定性，以及电离背景波动和星际介质有效状态方程对解释的影响。 2）最大化数据的科学回报：为此，该程序将解决红移失真问题（这既影响质量功率谱恢复程序，也影响通过相关函数的几何失真来测量宇宙常数的能力） ，参数之间的简并性（通过执行完全似然分析，这将揭示当前森林模型中 4 到 6 个自由参数的简并性），并更好地了解宇宙的热历史，（通过利用再电离后温度随时间的下降来推断或至少限制从温度测量中再电离的时代，使用红移在 2 到 4 之间的传输功率谱的小范围截止。）为该项目提供了资金由 NSF 河外天文学和宇宙学计划 (AST/EXC) 资助。***