Collaborative Research: Cosmology with the Lyman Alpha Forest

AST0098437Hui这是一个与纽约大学的Matias Zaldriaga(0098506)合作的研究项目。来自类星体(也称为类星体)的光通常在与中性氢红移的莱曼阿尔法线(静止波长1216埃)对应的位置上有多次强度下降或吸收线。这些通常以一系列吸收线的形式出现，称为莱曼阿尔法森林。红移是由宇宙的膨胀引起的。如果我们能计算出宇宙是如何膨胀的(基于宇宙学模型)，我们就能知道光子相对于我们的吸收位置。因此，我们可以使用吸收图来描绘类星体和我们之间的氢云的位置。与星系之类的物体相比，莱曼阿尔法星系中的云层质量并不是很大。正因为如此，可靠的计算机模拟(数值实验)才有可能从原始起伏中对它们的引力崩塌(形成)进行模拟。这些莱曼阿尔法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、墙壁和空洞)，从物质密度的微小波动开始，然后让重力和其他已知力作用。这些对物质结构和分布的详细计算是当前研究的前沿，这些计算机模拟方面的最新进展使人们有可能将红移在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。森林已经并将继续提供对许多量的有趣限制，例如原始质量功率谱的幅度和形状、中微子质量、物质密度、宇宙常数和再电离时代。这些限制，再加上其他观测的限制，为我们对宇宙学的基本理解提供了重要的检验。这个项目将主要集中在“传输功率谱”上，这是一种在宇宙学模型中使用的直接可观测的统计数字。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：确定森林中测量的波动时连续谱拟合的影响，用引力不稳定引起的质量波动来解释这些波动，以及电离背景和银河系间介质的有效状态方程的波动对解释的影响。2)最大化数据的科学回报：为此，该计划将处理红移失真(这既影响质量功率谱恢复程序，也影响通过关联函数的几何失真测量宇宙常数的能力)、参数之间的简并(通过执行完全似然分析，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，使用红移在2到4之间的传输功率谱的小范围截止的温度测量。)该项目的资金由NSF河外天文和AMP计划提供；宇宙学(AST/EXC)。*

ABSTRACT AST 0098437HuiThis is a Collaborative Research Project with Matias Zaldarriaga (0098506) of New York 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).***