Observational Cosmology by Observing Gravitational Lensing

支配宇宙的暗物质不会发出可探测的辐射，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。这些微弱的透镜畸变现在被用来测量一些丰富的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一个更大的半径。这是非常有趣的，因为理论n体模拟表明，星团的形状和轮廓对宇宙密度参数Omega的值和暗物质粒子的性质很敏感。一个特别有趣的例子是弱星团0957+561，它包含一个已知时间延迟的多重成像类星体。通过对星团质量的映射，改进了透镜的建模，得到了哈勃常数的改进值。这些观测的及时完成需要在望远镜上使用电荷耦合器件（CCD）马赛克相机。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相机。在天空中随机出现的弱引力透镜现象现在已经被初步探测到。数百万场星系的弱引力扭曲将被测量，这些测量的结果将提供明确的定量测量：8mpc尺度上的质量波动强度，线性摄动理论成立，波动与早期宇宙中的量子过程直接相关；功率谱在较小区域的斜率，用来区分目前不同的结构形成模型；在100kpc尺度上的功率谱，在那里将发现星系形成和暗物质晕的本质的线索；以及这些结构在宇宙最后三分之一的历史中增长的速度。这些测量只有在使用具有极大吞吐量的成像设备时才可行。大面积CCD （LACCD）马赛克相机将完成并安装在智利塞罗托洛洛美洲天文台（CTIO） 4米望远镜上，提供比那里任何其他仪器更大的吞吐量。这两个相机（在MDM和CTIO）将在这笔赠款下完成，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。博士学生将获得以前无法获得的仪器经验，选定的天文学本科专业学生将在密歇根和天文台站点使用仪器。对非理科生的导论课程进行改革，通过引入更多的现代实验练习和改进的课堂演示，强调提高学生的视觉化和解决问题的能力。这个项目的结果，以及其他天文系成员目前的结果，将通过每月全彩的“月度图像”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.