Understanding the Dark Components of the Universe

目前对宇宙大范围尺度和红移的观测似乎与单一的、标准的宇宙学模型一致。然而，这个模型的成分令人惊讶；它包括三个实验室物理未知的全新成分--膨胀场、暗能量和暗物质。确定这些新成分的真实性和本质仍然是宇宙学中最重要的任务之一。这一提议的目的是为了更好地理解主导晚期宇宙的两个成分--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。下面我将概述该计划的两个主要组成部分。在小尺度上关联暗物质和发光物质：我将重点讨论小尺度(银河系或银河系以下)暗物质结构，因为它的存在受到很好的限制，而且对不同暗物质候选者的预测在小尺度上存在分歧。我的团队目前正在参与一个项目，利用附近两个星系样本中的微弱光源的集群来探测孤立的类似银河系的星系周围的卫星群。初步结果显示，在这两种情况下，信号的信噪比均为10。我建议将这项工作扩展到更深层次的调查，以描述一组更大的初选周围的卫星数量。然后，我们将利用数值模拟，将观测到的卫星的丰度和分布与星系晕中暗物质亚结构的模型进行比较，以确定该理论是否与观测一致，如果是，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(恒星与晕质量比)的函数，在一个尚未被探索的区域。作为下一代处女座调查的一部分，我们最近完成了对处女座星系团核心预测结构和可见星系的初步比较。我计划将此研究扩展到整个群集卷。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。任何探测到的这种成分能量密度红移的变化都将为它的性质提供重要线索，但需要极其精确的(百分比水平)测量。我最近开发了一种经典宇宙学测试的新版本，测量一组引力透镜后面的平均透镜信号作为红移的函数。透镜信号的强度提供了一种间接的距离测量，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，我将这项测试应用于宇宙勘测中的星系群，将暗能量密度限制在12%以内。我建议将这一测试扩展到更大的CS82和CFHTLS调查，在这些调查中，应该可以将不确定度降低到3-4%或更少。我还在开发基于非线性结构形成的宇宙增长率测试。随着星系团的演化，星系团的内部松弛提供了一种估计其生长历史的方法。这反过来又会限制宇宙学结构的整体增长率，从而限制暗能量。鉴于目前和即将进行的调查预计会有大量关于集群的数据，这类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.