Understanding Biased Galaxy Formation

在过去的二十年里，天文学家已经积累了大量的证据，证明宇宙中存在一种看不见的成分，这种成分具有类似引力的影响，但没有其他可识别的特征。这种成分被称为“暗物质”。在构建宇宙模型的过程中，一个突出的问题是我们对暗物质相对于发光物质是如何分布的缺乏了解。描述这种分布差异的空间函数被称为“偏倚”，它的确定对于理解宇宙的结构和演化至关重要。该项目的目标是构建一系列宇宙学模型，使用被称为“晕占分布”（HOD）的偏差模型，该模型通过给出条件概率p（NjM）来定义星系群的偏差，该条件概率p（NjM）质量为M的暗物质晕包含N个星系，以及指定在虚化的暗晕内星系和暗物质的相对空间和速度分布的处方。这些模型将根据所使用的HOD来预测不同类型的星系群集。由这些宇宙学模型家族生成的预测星系分布将与澳大利亚（2dF星系红移调查或“2dFGRS”）和美国（斯隆数字巡天或“SDSS”）即将进行的调查中观测到的星系分布进行比较。这些比较可以确认模型的基本有效性，从而确定HOD的经验形式。或者，这些经验测试可能表明，目前关于星系形成的理论图景仍然缺少重要的物理成分。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

AST 0098584WeinbergOver the past two decades astronomers have amassed a considerable body of evidence for the existence of an unseen component of the universe which exerts a gravitational-like influence but has no other identified signature. This component is known as "dark matter." One of the outstanding problems in the construction of cosmological models is our lack of knowledge of just how the dark matter is distributed with respect to the luminous matter. The spatial function which can describe this difference in distribution is referred to as "bias" and its determination is critical for understanding the structure and evolution of the universe. The goal of this project is to construct a series of cosmological models, using a bias model known as the "halo occupation distribution" (HOD) which defines the bias of a population of galaxies by giving the conditional probability p(NjM) that a dark matter halo of virial mass M contains N galaxies, together with prescriptions that specify the relative spatial and velocity distributions of galaxies and dark matter within virialized dark halos. These models would predict different types of galaxy clustering depending on the HOD used. The resulting predicted distributions of galaxies generated by these families of cosmological models will be compared with the observed galaxy distributions found in the upcoming surveys from Australia (the 2dF Galaxy Redshift Survey or "2dFGRS") and from the United States (the Sloan Digital Sky Survey or "SDSS"). These comparisons may confirm the basic validity of the models and thus determine an empirical form of the HOD. Alternatively, these empirical tests may show that the current theoretical picture of galaxy formation is still missing important physical ingredients. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC).***