Accurate cosmology from the Dark Energy Survey

任何望远镜都无法直接观测到暗物质和暗能量，但它们引起了人们极大的兴趣，因为它们构成了宇宙中96%的质能。目前任何物理理论都无法完全预测或描述暗物质和暗能量。在智利的4米布兰科望远镜上进行的暗能量调查（DES）旨在高精度地测量这些暗成分的特性，并确定广义相对论在大尺度上是否正确。该项目将重点解决DES面临的三个问题：统一校准调查获得的10万张星系图像（提供10倍的改进）；提供准确的红移（仅基于图像，而不是光谱）；通过测量星系形状的细微扭曲来精确地确定暗物质的分布。这项工作将提高DES观测的质量，这样科学家就可以更好地测量暗物质和能量的性质，以及其他被观测到的天文物体的性质。除了这些科学目标之外，该项目还将与来自各种教育背景的本科生合作，培养STEM能力。此外，该计划还包括与富兰克林研究所建立新的合作伙伴关系，通过富兰克林的“城市天空”旅行天文学计划向费城的社区组织和中学教师提供服务，并为教师举办讲习班。City Skies关注的是历史上服务不足的内城社区。城市天空项目的目标是开发有关天文主题的课程材料和报告。来自当前项目的支持将允许PI扩展与Franklin的工作。这个项目显然与美国国家科学基金会促进科学进步的使命有关。此外，该项目的“更广泛的影响”部分做到了这一点，并通过帮助培养对下一代不同个人的STEM活动的兴趣和教育来促进国家的健康、繁荣和福利。DES是200多名科学家的国际合作项目，使用美国能源部资助的5亿像素相机，以5种颜色拍摄南方天空的四分之一，相机安装在智利Cerro Tololo的国家科学基金会资助的Blanco 4米望远镜上。这些图像如何测量既不发光也不吸收光的东西呢？首先，暗物质的引力使宇宙中可见的5%发出的光弯曲，导致可见物体的形状发生微妙的扭曲。最终的DES数据将使用“弱引力透镜”（WL）特征对2亿个星系的形状进行测量，以约1%的精度测量暗物质的聚集。暗物质和能量的第二个引力特征是它们驱动可见星系的运动，因此它们的位置和红移（距离）的统计数据限制了暗成分；这在与WL信息结合使用时尤其强大。这项建议的重点是解决DES在充分发挥这些测量的潜力方面面临的三个最困难的问题。第一个挑战是对5年内拍摄的10万张不同图像进行统一校准：它将从目前的1%提高到接近0.1%的水平，这是在以前的NSF支持下，在调查的一个晚上实现的。第二个挑战是将WL签名测量到千分之一的精度：提出者已经开发了第一个实用的算法来在模拟数据上达到这种精度，并建议改进它并应用于DES图像。调查的第三个困难部分是在没有对每个来源进行光谱观测的情况下精确地分配星系红移。提出将光度红移估计和透镜测量整合为一个过程，严格处理噪声和选择效应，产生一个联合红移/透镜后验概率。这反过来又为分析DES数据提供了一种新技术，通过创建与所有观测到的星系位置、形状和颜色一致的暗物质密度图集合。

Dark matter and dark energy cannot be directly observed with any telescope, but are of great interest because they make up 96% of the mass-energy in the Universe. Neither dark matter nor dark energy is fully predicted or described by any current physical theory. The Dark Energy Survey (DES), being conducted on the 4-meter Blanco telescope in Chile, is designed to measure the properties of these dark components to high precision, and determine whether General Relativity is the correct theory of gravity on large scales. This project will focus on solving three problems that the DES faces: uniformly calibrating the 100,000 galaxy images obtained by the survey (providing an improvement of 10x); providing accurate redshifts (based on images only, not spectroscopy); and measuring the subtle distortions of the shapes of galaxies to high accuracy to determine the distribution of dark matter. This work will then enhance the quality of the DES observations so that scientists can better measure the properties of dark matter and energy, as well as those of the other astronomical objects being observed.Besides these scientific objectives, the project will work with undergraduates (from a variety of educational backgrounds) to develop STEM capabilities. In addition, this program includes a new partnership with the Franklin Institute for outreach to community-based organizations and middle-school teachers in Philadelphia through Franklin's "City Skies" traveling astronomy program and hosted workshops for teachers. City Skies has a focus on historically underserved inner-city neighborhoods. The City Skies project targets development of curricular materials and presentations on astronomical topics. Support from the current project will allow the PI to extend work with Franklin. This project clearly relates to NSF's mission to promote the progress of science. In addition, the "Broader Impact" portion of the project does this, and advances the national health, prosperity and welfare by helping to develop interest in, and educating, STEM activities among the next generation of diverse individuals.DES is collaborative international effort of more than 200 scientists to image one quarter of the Southern sky in 5 colors using a DOE-funded 500 Mpixel camera installed on the NSF-funded Blanco 4-meter telescope on Cerro Tololo, Chile. How can these images measure things that neither emit nor absorb light? First, the dark matter's gravity bends the light emitted by the 5% of the Universe that is visible, causing subtle distortions in the shapes of visible objects. The final DES data will use the "weak gravitational lensing" (WL) signature on the shapes of 200 million galaxies to measure the clustering of dark matter to ~1% accuracy. A second gravitational signature of dark matter and energy is that they drive the motions of the visible galaxies, so that the statistics of their positions and redshifts (distances) constrain the dark components; this is especially powerful in combination with the WL information. This proposal focuses on solving three of the most difficult problems that DES faces in reaching its full potential for these measurements. The first challenge is uniform calibration of 100,000 different images taken over 5 years: it will be improved from the current 1% state of the art to near the 0.1% level that was achieved for single nights of the survey using previous NSF support. A second challenge is to measure the WL signature to part-per-thousand accuracy: the proposers have developed the first practical algorithm to attain this accuracy on simulated data, and propose to improve it and apply to the DES images. The third difficult part of the survey is assigning accurate galaxy redshifts without spectroscopic observations of each source. It is proposed to integrate the photometric redshift estimation and lensing measurement into a single process that rigorously treats noise and selection effects to produce a single joint redshift/lensing posterior probability. This in turn enables a new technique for analyzing DES data by creating an ensemble of maps of dark matter density that are consistent with all of the observed positions, shapes, and colors of the galaxies.