Cosmic Flexion

爱因斯坦相对论的伟大预言之一是，光可以被恒星和星系等大质量天体所弯曲。这种现象被称为引力透镜，可以使相对较近的物体看起来拉伸和扭曲，就像通过放大镜的边缘看到的一样。通过解释这些扭曲，就有可能找出产生透镜的物质的位置。德雷克塞尔大学的科学家的目标是通过观察大约1亿个星系的形状来测量宇宙中暗物质的质量分布。由于彼此靠近的星系也经历了类似的扭曲，因此可以推断暗物质的真实位置和分布。从科学上讲，这项工作具有广泛的影响，因为它处理了物质如何在小范围内演化的最基本的问题。作为该项目的一部分，该团队还将开发一个针对费城高中生的宇宙学暑期学校。这项工作涉及使用暗能量调查(DES)首次测量宇宙从大尺度结构到受限程度较低的非线性区域的弯曲。这种方法是以宇宙剪切测量为模型的，在宇宙剪切测量中，成对星系的透镜信号是相关的。引力弯曲(图像的“弧度”)等于暗物质密度场的梯度，对小尺度扰动特别敏感。宇宙切变测量了从2角分到几度的尺度结构。相比之下，大尺度结构的宇宙弯曲分析可以在2到20角秒的范围内对非线性功率谱产生约束，对应于几十个千帕秒的尺度。该团队还将测量弯曲-剪切关联函数，该函数将产生从几角秒到10角分钟的信号，弥合宇宙剪切和弯曲两个区域之间的差距。最后，同样的数据集和简化可以并将被应用于估计单个星系-星系透镜信号并产生对星系质量函数的约束。研究小组将利用他们的专业知识开发可供更广泛的社区使用的工具，除了提供对小尺度宇宙结构的直接估计之外。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

One of the great predictions of Einstein's Theory of Relativity is that light can be bent by massive, astrophysical objects like stars and galaxies. This phenomenon, known as gravitational lensing, can cause relatively nearby objects to appear stretched and distorted, as if seen through the edges of a magnifying glass. By interpreting those distortions, it is possible to figure out the location of matter creating the lensing. Scientists at Drexel University aim to measure the mass distribution of dark matter in the universe by looking at the shapes of approximately 100 million galaxies. Since galaxies that are near one another also experience similar distortions, the true location and distribution of dark matter can be inferred. Scientifically, this work has a broad impact as it deals with the most fundamental questions of how matter evolves on small scales. As part of this project, the team will also develop a Cosmology Summer School aimed at Philadelphia high school students.This work involves the first measurement of Cosmic Flexion from large-scale structure, well into the poorly constrained, nonlinear regime, using the Dark Energy Survey (DES). This approach is modeled on cosmic shear measurements in which the lensing signals of pairs of galaxies are correlated. Gravitational flexion (the ``arciness'' of an image) is equal to the gradient of the dark matter density field and is particularly sensitive to small scale perturbations. Cosmic shear measures structure on scales from 2 arcminutes up to several degrees. By comparison, cosmic flexion analysis of large-scale structure can produce constraints on the nonlinear power spectrum from 2 to 20 arcseconds, corresponding to the tens of kilosparsecs scale. The team will also measure flexion-shear correlation functions, which will produce signals ranging from several arcseconds to 10 arcminutes, bridging the gap between the two regimes of cosmic shear and flexion. Finally, the same dataset and reduction can and will be applied to estimate individual galaxy-galaxy lensing signals and produce constraints on galaxy mass functions.The research team will utilize their expertise to develop tools which can be used by the broader community, in addition to providing direct estimates of small-scale cosmic structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.