Observational Cosmology by Observing Gravitational Lensing

AST 9624592 摘要-伯恩斯坦 支配宇宙的暗物质不发射可探测的辐射，但通过光线的引力偏转会扭曲背景物体的图像。研究计划是测量这些“弱引力透镜”效应，以确定星系团的真实形状和当今宇宙中质量波动的光谱。 这些微弱的透镜扭曲现在被用来测量一些丰富星系团内部的质量分布。 10个星系团的质量分布将被测量到更大的半径。 这是非常有趣的，因为理论N体模拟表明，集群的形状和配置文件是敏感的宇宙学密度参数Ω的值，和暗物质粒子的性质。 一个特别有趣的例子是弱星系团0957+561，它包含一个具有已知时间延迟的多重成像类星体。 通过对星团质量的映射，将改进该透镜的建模，并将获得改进的哈勃常数值。 要及时完成这些观测，需要在具有良好视宁度的望远镜上使用电荷耦合器件（CCD）镶嵌照相机。 将为密歇根-达特茅斯-麻省理工学院（MDM）2.4米望远镜建造一个CCD照相机。 在天空的随机部分的弱引力透镜现在已经被初步探测到。 将测量数百万个场星系的弱引力畸变，这些测量的结果将提供明确的定量测量：在8 Mpc尺度上的质量波动强度，其中线性微扰理论成立，波动与早期宇宙中的量子过程直接相关;较小区域中功率谱的斜率，其区分结构形成的当前竞争模型;在100千秒差距尺度上的功率谱，将发现星系形成和暗物质晕的性质的线索;以及这些结构在宇宙历史上最后三分之一的增长率。 这些测量只有在使用具有极大吞吐量的成像设备时才是可行的。 大面积CCD（LACCD）镶嵌照相机将完成并安装在智利Cerro Tololo Interamerican Observatory（CTIO）4米望远镜上，其吞吐量比那里的任何其他仪器都大。 这两台相机（在MDM和CTIO）将在此赠款下完成，将成为设施仪器，并提供给其他天文学家。 完成的仪器还将用于加强密歇根大学学生的教育。 Ph. D.学生将获得以前没有的仪器经验，和选定的本科天文学专业将与密歇根州和天文台网站的仪器工作。 为非理科本科生而设的入门课程亦会作出修订，重点是透过引入更现代化的实验练习及改善课堂示范，提高学生的想像力及解决问题的能力。 该计划的结果，以及其他天文系成员目前的结果，将通过每月的全彩“每月图像”俱乐部邮件传达给密歇根州的高中科学教师和学生。

AST 9624592 Abstract - Bernstein The dark matter which dominates the Universe does not emit detectable radiation, but does distort images of background objects by the gravitational deflection of the passing light rays. The research plan is to measure these "weak gravitational lensing" effects to determine the true shapes of galaxy clusters and the spectrum of the mass fluctuations in the present-day Universe. These weak lensing distortions are now being used to measure the mass distributions of the inner parts of a few rich clusters of galaxies. The mass profiles of 10 clusters of galaxies will be measured to a larger radius. This is of great interest since theoretical N-body simulations show that cluster shapes and profiles are sensitive to the value of the cosmological density parameter Omega, and to the nature of the dark matter particles. A particularly interesting case is the weak cluster 0957+561, which contains a multiply-imaged quasar with known time delay. By mapping the cluster mass, the modeling of this lens will be improved and an improved value for the Hubble constant will be obtained. The timely completion of these observations requires the use of a Charged Coupled Device (CCD) mosaic camera on a telescope with good seeing. A CCD camera for the Michigan-Dartmouth-MIT (MDM) 2.4m telescope will be constructed. Weak gravitations lensing in random parts of the sky has now been tentatively detected. The weak gravitational distortions of several million field galaxies will be measured, the results from these measurements will provide unambiguous quantitative measurements of: the strength of mass fluctuations on 8 Mpc scales, where linear perturbation theory holds and the fluctuations are directly related to quantum processes in the early Universe; the slope of the power spectrum in the in smaller regions, which distinguishes between present rival models of the structure formation; the power spectrum on 100 kpc scales, where clues to the nature of galaxy formation and dark matter halos will be found; and the growth rate of these structures over the last third of the history of the Universe. These measurements are only feasible if imaging devices with extremely large throughput are used. The Large Area CCD (LACCD) mosaic camera will be completed and mounted on the Cerro Tololo Interamerican Observatory (CTIO) 4m telescope in Chile, giving larger throughput than any other instrument there. Both cameras (at MDM and CTIO) to be completed under this grant will become facility instruments and made available to other astronomers. The completed instruments will also be used to enhance the education of students at the University of Michigan. Ph. D. students will obtain previously unavailable instrumentation experience, and selected undergraduate astronomy majors will work with instruments in Michigan and at observatory sites. The introductory courses for non-science major undergraduates will be revamped, with an emphasis on improving the students' visualization and problem-solving abilities by introducing more modern laboratory exercises and improved classroom demonstrations. The results of this program, and current results by other Astronomy Department members, will be communicated to high school science teachers and students throughout the State of Michigan via a monthly full-color "Image-of-the-Month" club mailing.