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测，但人们对它们非常感兴趣，因为它们占宇宙质量能量的96%。目前的任何物理理论都不能完全预测或描述暗物质和暗能量。暗能量调查(DES)是在智利的4米布兰科望远镜上进行的，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的正确引力理论。这个项目将重点解决DES面临的三个问题：统一校准通过调查获得的100,000张星系图像(改进10倍)；提供精确的红移(仅基于图像，而不是光谱)；高精度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，以便科学家能够更好地测量暗物质和能量的性质，以及其他被观测的天文物体的性质。除了这些科学目标，该项目还将与来自不同教育背景的本科生合作，发展STEM能力。此外，该计划还与富兰克林研究所建立了新的合作伙伴关系，通过富兰克林的“城市天空”巡回天文计划与费城的社区组织和中学教师建立联系，并为教师举办研讨会。City Skies将重点放在历史上服务不足的市中心社区。城市天空项目的目标是开发关于天文主题的课程材料和演讲。当前项目的支持将使PI能够延长与富兰克林的合作。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，并通过帮助在下一代不同的个人中培养对STEM活动的兴趣和教育来促进国家的健康、繁荣和福利。DES是由200多名科学家合作的国际努力，使用安装在智利塞罗托洛的NSF资助的Blanco 4米望远镜上的一台由能源部资助的500兆像素相机以5种颜色拍摄南方天空的四分之一。这些图像如何测量既不发光也不吸收光的东西呢？首先，暗物质的引力会弯曲可见宇宙5%发出的光，导致可见物体形状的微妙扭曲。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性，准确度为1%。暗物质和暗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；这一点与WL信息结合起来尤其强大。这项提议的重点是解决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%的最先进水平提高到接近0.1%的水平，这是使用之前的NSF支持在调查的单个晚上实现的。第二个挑战是将WL签名的精度测量到千分之几的精度：提出了第一个实用的算法来在模拟数据上达到这个精度，并建议对其进行改进并应用于DES图像。调查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指定准确的星系红移。建议将光度红移估计和透镜测量集成到一个过程中，该过程严格处理噪声和选择效应，以产生单一的联合红移/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，方法是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。

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.