Gravity in the crossfire: A weak lensing study of merging and relaxed galaxy clusters

几十年来，星系团和星系团的引力透镜一直被用作重子和暗物质的探测器，而且它们的使用还在不断成熟。然而，在未来的调查中，它们在限制宇宙学参数方面的使用目前受到巨大的系统学误差的限制。弱透镜切变测量的误差需要改善一个数量级，星系团的质量测定需要对非维尼化结构进行可靠的修正。该项目旨在将对星系团中弱透镜的观测测量与对弱透镜图像的真实模拟相结合，目的是充分了解上述系统误差，从而使弱透镜和星系团质量研究能够导致精确和可靠的宇宙学参数测量。具体地说，研究人员计划如下：(1)在Bullet星系团研究的先前成功的基础上，利用已知的星系团合并和搜索未知的星系团合并来确定大距离引力是否真的遵循平方力反比定律。其目的是排除重力模型与部分经典和部分替代的“混合”模式。(2)在选择接近维里平衡的星团样本上，使用四种不同的技术来确定星团质量和确定它们的一致性。其目的是提供修正系数和/或统计数据，以查明任何有偏见或有问题的技术，并从整个科学界的现有目录中查明和消除问题组。(3)将观测测量与模拟相结合，以确定图像所有部分的点扩展函数(PSF)的精度。这项工作旨在成为更大的国际模拟计划“STEP”的一部分，为未来的测量提供准确的模拟。在教育方面，该项目通过直接参与研究和现代研究工具的技术培训，为三名本科生和三名研究生提供培训。此外，该项目还包括一个教育和公共推广计划，目的是通过公共推广活动和利用该项目中获得的数据开发一个新的天文学入门课程，提高俄亥俄州、西弗吉尼亚州和肯塔基州等阿巴拉契亚地区历史上服务不足的地区的科学素养。

Clusters of galaxies and gravitational lensing by clusters of galaxies have been used as probes of baryonic and dark matter for several decades, and their use continues to mature. However, their use in constraining cosmological parameters in future surveys is currently limited by large systematics errors. Errors in weak lensing shear measurements need to improve by an order of magnitude, and masses determinations of clusters of galaxies need reliable corrections for non-virialized structures. This project intends to combine observational measurements of weak lensing in galaxy clusters with realistic simulations of weakly lensed images with the goal of gaining sufficient understanding of the above systematic errors to allow weak lensing and cluster mass studies to lead to precise and reliable measurements of cosmological parameters.Specifically, the investigators plan the following: (1) Building on previous success from the Bullet Cluster study, to use known cluster mergers and search for unknown ones to determine whether gravity at large distances really does follow an inverse square force law. The intent is to rule out models of gravity "mixed" with part classical and part alternative. (2) To use four different techniques on a sample of clusters, chosen to be close to virial equilibrium, to determine clusters masses and determine their consistency. This intent is to provide correction factors and/or statistics to identify any biased or problematic techniques and to identify and eliminate problem clusters from existing catalogues for the entire scientific community. (3) To combine observational measurements with simulations to what precision a point spread function (PSF) can be determined in all parts of an image. This work is intended to be part of larger international simulation program called "STeP" to provide accurate simulations for future surveys.Educationally, this project provides training for three undergraduate and three graduate students through direct involvement in research and technical training in modern research tools. In addition, this project includes an education and public outreach program with the goal of increasing scientific literacy in the historically underserved Appalachian regions of Ohio, West Virginia, and Kentucky through a combination of public outreach events and the development of a new laboratory component to an introductory astronomy class that makes use of the data obtained in this project.