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: 0098506
• 负责人: Matias Zaldarriaga
• 金额: $ 5.98万
• 依托单位: New York University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-07-01 至 2003-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0098506&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).***

这是与哥伦比亚大学的Lam Hui（0098437）的合作研究项目。类星体（也称为类星体）发出的光通常在与中性氢的红移莱曼α线（静止波长1216埃）相对应的位置上具有多个强度下降或吸收线。这些通常以一系列吸收线的形式出现，称为莱曼α森林。红移是由宇宙膨胀引起的。如果我们能计算出宇宙是如何膨胀的（基于宇宙学模型），我们就能知道光子是在哪里被吸收的。因此，我们可以利用吸收图来绘制介于类星体和我们之间的氢云的位置。莱曼α星系中的云与星系等物体相比质量并不大。正因为如此，它们从原始波动中的引力坍缩（形成）的可靠计算机模拟（数值实验）是可能的。这些莱曼阿尔法森林模拟产生的结构类似于我们在附近的宇宙中看到的（细丝，墙壁和空隙），从物质密度的微小波动开始，然后让重力和其他已知的力量起作用。这些对物质结构和分布的详细计算是当前研究的前沿，而计算机建模的这些最新进展使人们有可能使用在红移2和4之间的莱曼α森林的观测作为强大的宇宙学工具。森林提供了，并将继续提供，有趣的约束，许多数量，如振幅和形状的原始质量功率谱，中微子质量，物质密度，宇宙学常数，和再电离时代。这些限制，与其他观测的限制一起，为我们对宇宙学的基本理解提供了重要的检查。本项目将主要集中在“传输功率谱”，这是一种用于宇宙学模型的统计数据，可以直接观察到。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方面的影响，这些波动的解释是由引力不稳定性引起的质量波动，以及电离背景波动和星系际介质有效状态方程对解释的影响。2)从数据中获得最大的科学回报：为此，该计划将解决红移失真，（这既影响了质量功率谱恢复的程序，也影响了通过相关函数的几何失真来测量宇宙常数的能力），参数间退化（通过执行全似然分析，这将揭示当前森林模型中4到6个自由参数的退化），以及更好地了解宇宙的热历史（通过使用再电离后温度随时间的下降来推断或至少限制再电离的时期，从使用在2和4之间的红移处的透射功率谱的小尺度截止的温度测量。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。