Accurate cosmology from the Dark Energy Survey

暗物质和暗能量不能用任何望远镜直接观察到，但它们非常感兴趣，因为它们占宇宙质量能量的96%。 无论是暗物质还是暗能量都没有被任何现有的物理理论完全预测或描述。暗能量调查（DES）正在智利的4米布兰科望远镜上进行，旨在高精度地测量这些暗成分的性质，并确定广义相对论是否是大尺度上正确的引力理论。 该项目将专注于解决DES面临的三个问题：统一校准调查获得的10万个星系图像（提供10倍的改进）;提供准确的红移（仅基于图像，而不是光谱学）;以及测量星系形状的细微扭曲以确定暗物质的分布。 这项工作将提高DES观测的质量，使科学家能够更好地测量暗物质和能量的性质，以及正在观察的其他天体的性质。除了这些科学目标，该项目还将与大学生（来自各种教育背景）合作，培养STEM能力。 此外，该方案还包括与富兰克林研究所建立新的伙伴关系，通过富兰克林的“城市天空”旅行天文学方案和为教师举办的讲习班，向费城的社区组织和中学教师进行宣传。城市天空的重点是历史上服务不足的市中心社区。城市天空项目的目标是编制天文学专题的教材和介绍。当前项目的支持将使PI能够扩展与富兰克林的工作。 这个项目显然与NSF的使命，以促进科学的进步。 此外，该项目的“更广泛的影响”部分做到了这一点，并通过帮助发展对以下方面的兴趣和教育，DES是200多名科学家的国际合作努力，使用安装在NSF上的DOE资助的500 Mpixel相机，以5种颜色对南部天空的四分之一进行成像。智利托洛洛山上的布兰科4米望远镜。这些图像如何测量既不发光也不吸收光的东西？首先，暗物质的引力使可见的宇宙的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2亿个星系形状上的“弱引力透镜”（WL）特征来测量暗物质的聚集，精确度约为1%。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;这与WL信息结合起来特别强大。该建议的重点是解决DES在充分发挥这些测量潜力时面临的三个最困难的问题。第一个挑战是对5年内拍摄的100，000张不同图像进行统一校准：它将从目前的1%最先进水平提高到接近0.1%的水平，这是在以前的NSF支持下在调查的单个夜晚实现的。第二个挑战是测量WL签名到千分之一的精度：提议者已经开发了第一个实用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。巡天的第三个困难部分是在没有对每个源进行光谱观测的情况下，确定准确的星系红移。建议将光度红移估计和透镜测量集成到一个单一的过程中，严格对待噪声和选择效应，产生一个单一的联合红移/透镜后验概率。这反过来又使一种新的技术，用于分析DES数据，通过创建一个暗物质密度的整体地图，与所有观察到的星系的位置，形状和颜色一致。

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.