Understanding the Dark Components of the Universe

目前对大范围尺度和红移的宇宙观测似乎与宇宙学的单一标准模型相一致。然而，这种模式的成分令人惊讶；它包含了实验室物理学中未知的三个全新成分——暴胀场、暗能量和暗物质。确定这些新成分的真实性和性质仍然是宇宙学中最重要的任务之一。这项提议的目的是为了更好地理解主宰晚期宇宙的两种成分——暗能量和暗物质，并确定暗结构和发光结构之间的关系。这些方法将包括结构形成的数值模拟，局部星系分布的统计分析，以及基于引力透镜的宇宙学测试。我将在下面概述该计划的两个主要组成部分。在小尺度上联系暗物质和发光物质：我将重点关注小尺度（星系或亚星系）暗物质结构，因为它的存在很少受到约束，而且由于对不同暗物质候选者的预测在小尺度上存在分歧。我的团队目前正在从事一个项目，利用两个附近星系样本中的微弱源聚集来探测孤立的类银河系星系周围的卫星群。初步结果表明，在两种情况下，聚类信号的信噪比均为~10。我建议将这项工作扩展到更深入的调查，以表征围绕更大一组主要卫星的卫星数量。通过数值模拟，我们将把观测到的卫星的丰度和分布与星系晕中暗物质子结构的模型进行比较，以确定该理论是否与观测结果一致，如果是的话，卫星如何在小尺度上追踪暗物质。结合理论和观测，我们将测量星系形成的净效率，作为暗物质晕质量（恒星与晕的质量比）的函数，在一个尚未被探索的制度下。我们最近完成了室女座星系团核心的预测结构和可见星系之间的初步比较，作为下一代室女座调查的一部分。我计划将这项研究扩展到整个集群卷。这些研究应该为不同环境下的星系形成和演化模型提供一个更精确的框架。限制暗能量：目前对暗能量的观测与宇宙常数一致，这是一种简单的可能性，但很难解释。任何检测到的该成分能量密度的红移变化都将为其性质提供重要线索，但需要极其精确（百分比级别）的测量。我最近开发了一个经典宇宙学测试的新版本，测量一组引力透镜背后的平均透镜信号作为红移的函数。透镜信号的强度提供了距离的间接测量，由此产生的距离-红移关系限制了膨胀历史，从而限制了暗能量。作为概念的证明，我将这个测试应用于COSMOS调查中的星系群，将暗能量密度限制在12%以内。我建议将此测试扩展到更大的CS82和CFHTLS调查，其中应该有可能将不确定性降低到3-4%或更少。我也在开发基于非线性结构形成的宇宙增长率测试。星系团在演化过程中的内部松弛提供了一种估计其生长历史的方法。反过来，这可以限制宇宙结构的整体增长速度，从而限制暗能量。鉴于目前和即将进行的调查预计会提供关于群集的大量数据，这种测试正变得越来越重要。

Current observations of the universe over a wide range of scales and redshifts seem consistent with a single, standard model of cosmology. The ingredients of this model are surprising, however; it includes three radically new components, unknown from laboratory physics - an inflationary field, dark energy, and dark matter. Establishing the reality and nature of these new components remains one of the most important tasks in cosmology.The aim of this proposal is to better understand the two components - dark energy and dark matter - that dominate the late-time universe, and to determine how dark and luminous structures are related. The methods will include numerical simulations of structure formation, statistical analyses of the local galaxy distribution, and cosmological tests based on gravitational lensing. I outline the two main components of the program below. Relating Dark and Luminous Matter on Small Scales:I will focus on small-scale (galactic or subgalactic) dark matter structure, since its existence is poorly constrained, and since predictions for different dark matter candidates diverge on small scales. My group is currently engaged in projects using the clustering of faint sources in two nearby galaxy samples to detect satellite populations around isolated Milky Way-like galaxies. The initial results show a clustering signal at signal-to-noise ~10 in both cases. I propose to extend this work to deeper surveys, to characterize the population of satellites around a larger set of primaries. Using numerical simulations, we will then compare the abundance and distribution of observed satellites to models of dark matter substructure in galaxy halos, to determine whether the theory is consistent with observations, and if so, how satellites trace dark matter on small scales. Combining theory and observations, we will measure the net efficiency of galaxy formation as a function of dark matter halo mass (the stellar-to-halo mass ratio) in a regime where it has not yet been explored. We have recently completed an initial comparison between predicted structure and visible galaxies in the core of the Virgo cluster, as part of the Next Generation Virgo Survey. I plan to extend this study to the entire cluster volume. These studies should provide a more precise framework for models of galaxy formation and evolution in different environments.Constraining Dark Energy:Current observations of dark energy are consistent with a cosmological constant, a simple possibility but a difficult one to explain. Any detected variation with redshift in the energy density of this component would provide a vital clue to its nature, but extremely precise (percent-level) measurements are required. I recently developed a new version of a classic cosmological test, measuring the mean lensing signal behind a set of gravitational lenses as a function of redshift. The strength of the lensing signal provides an indirect measure of distance, and the resulting distance-redshift relation constrains the expansion history and thus dark energy. As a proof of concept, I have applied this test to galaxy groups in the COSMOS survey, constraining the dark energy density to within 12%. I propose to extend this test to the larger CS82 and CFHTLS surveys, where it should be possible to reduce the uncertainties to 3-4% or less. I am also developing tests of the cosmic growth rate based on non-linear structure formation. The internal relaxation of galaxy clusters as they evolve provides a means of estimating their growth history. This, in turn, can constrain the overall growth rate of cosmological structure, and thus dark energy. Such tests are becoming increasingly important, given the wealth of data on clusters expected from current and forthcoming surveys.