Understanding Biased Galaxy Formation

在过去的二十年里，天文学家积累了大量证据，证明宇宙中存在一种看不见的组成部分，它施加着类似引力的影响，但没有其他可识别的特征。这种成分被称为“暗物质”。构建宇宙学模型的一个突出问题是我们缺乏关于暗物质相对于发光物质的确切分布的知识。能够描述这种分布差异的空间函数被称为“偏差”，它的确定对于理解宇宙的结构和演化至关重要。这个项目的目标是建立一系列的宇宙学模型，使用被称为“晕占据分布”(HOD)的偏差模型，该模型通过给出维里质量为M的暗物质晕包含N个星系的条件概率p(NJM)，以及指定星系和维里化暗晕内暗物质的相对空间和速度分布的处方来定义星系群的偏差。这些模型将根据所使用的HOD来预测不同类型的星系团。由这些宇宙学模型家族产生的星系的预测分布将与澳大利亚(2DF星系红移调查或“2dFGRS”)和美国(斯隆数字天空调查或“SDSS”)即将进行的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，目前星系形成的理论图景仍然缺乏重要的物理因素。该项目的资金由NSF河外天文与宇宙学计划(AST/EXC)提供。*

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).***