Collaborative Research: Cosmology with the Lyman Alpha Forest

AST 0098506zaldarriaga与哥伦比亚大学林慧（0098437）合作研究项目。来自类星体（也称为qso）的光通常在强度或吸收线上有多个下降，在与中性氢红移的莱曼α线（静止波长1216埃）对应的位置。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（基于宇宙模型），我们就能知道光子被吸收的位置与我们的关系。因此，我们可以使用吸收图来绘制类星体和我们之间的中间氢云的位置。莱曼α系统中的云与星系之类的物体相比，质量并不大。正因为如此，可靠的计算机模拟（数值实验）它们的引力坍缩（形成）从原始波动是可能的。这些莱曼α森林模拟产生了类似于我们在附近宇宙中看到的结构（细丝、壁和空洞），从物质密度的微小波动开始，然后让重力和其他已知的力起作用。这些对物质结构和分布的详细计算是当前研究的前沿，计算机建模的这些最新进展使得利用红移在2和4之间的莱曼α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许多有趣的限制，如原始质量功率谱的振幅和形状、中微子质量、物质密度、宇宙常数和再电离时代。这些约束，连同来自其他观测的约束，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“发射功率谱”，这是一种用于宇宙模型的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，以解决以下问题：连续拟合在确定森林中测量的波动方面的影响，根据引力不稳定性引起的质量波动来解释这些波动，以及电离背景波动和星系间介质的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，该计划将解决红移畸变（影响质量功率谱恢复计划，以及通过相关函数的几何畸变测量宇宙常数的能力），参数之间的简并（通过执行全似然分析，将揭示当前森林模型中4至6个自由参数的简并），并获得对宇宙热历史的更好理解。（利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代，方法是利用在2和4之间红移处透射功率谱的小尺度截止来测量温度。）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 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).***