A New Instrument to Remove the Effects of Interstellar Dust Masking Faint Radiation in the Universe

早期宇宙理论预测宇宙微波背景辐射中有一个非常微弱的极化信号。然而，来自银河系星际云和磁场的更强信号阻止了科学家测量这种微弱信号。恒星之间的空间包含许多这样的气体云和尘埃云。戏剧性的天文图像揭示了它们——例如，猎户座的大星云或著名的鹰状星云。星际云中的尘埃颗粒也会微弱地极化反射的星光。为了找到星际云，天文学家可以测量这种弱偏振。在这个项目中，研究人员将建造一个新的仪器来测量星际尘埃云产生的光偏振。利用这些测量数据和宇宙飞船的数据，他们将绘制出银河云和磁场的位置。然后，科学家们可以将它们的信号与宇宙微波背景辐射分离开来。这个项目增加了我们对早期宇宙的认识，符合国家利益。研究人员将包括一个由本科生、研究生和博士后组成的国际团队，参与该项目的各个方面，从而产生更广泛的影响。研究人员将设计并建造一种新型的广域线性光学偏振计（WALOP），并将使用该仪器测量由星际尘埃引起的偏振，并绘制银河系尘埃分布图。在30 x 30弧分的视场中，偏振计将形成每颗恒星的四幅同时图像，从而确定每个物体的星等、分数偏振和偏振角。它将被部署在南非天文台（SAAO）的1米望远镜上。结合GAIA航天器的距离测量，极化数据将实现星际介质的三维断层扫描，提供的信息可能使科学家能够从宇宙微波背景（CMB）中提取出非常微弱的极化信号。这项工作的智力价值主要来自于这样一个事实，即改进了银河系尘埃分布的映射，可能使天文学家能够在CMB辐射中探测到预测的弱极化信号（所谓的“b模式”信号），从而大大提高了宇宙学家对早期宇宙的理解。观测还将提高天文学家对银河系中尘埃形成、演化、组成和磁场排列的理解。研究人员计划在加州理工学院、印度IUCAA、SAAO和希腊克里特岛大学为本科生、研究生和博士后提供强有力的项目，将仪器开发与尖端天体物理学和宇宙学项目结合起来，并包括合作机构之间的互访。

Theories of the early Universe predict a very weak polarization signal in the cosmic microwave background radiation. However, stronger signals from interstellar clouds and magnetic fields in our Milky Way Galaxy prevent scientists from measuring that faint signal. The space between the stars contains many such clouds of gas and dust. Dramatic astronomical images reveal them - for example, the Great Nebula in the constellation Orion or the famous Eagle Nebula. Dust grains in the interstellar clouds also polarize reflected starlight weakly. Astronomers can measure this weak polarization in order to find the interstellar clouds. In this project, the Investigators will construct a novel instrument to measure the optical polarization produced by interstellar dust clouds. Using these measurements with spacecraft data, they will map the locations of Galactic clouds and magnetic fields. Scientists can then separate their signals from the cosmic microwave background radiation. This project serves the national interest by increasing our knowledge of the early Universe. The Investigators will involve an international team of undergraduates, graduate students, and postdocs in all aspects of this project, giving it strong Broader Impacts.The Investigators will design and build a novel wide-area linear optical polarimeter (WALOP) and will use the instrument to measure polarization caused by interstellar dust and to map the distribution of dust in the Milky Way Galaxy. With a 30 x 30 arcminute field of view, the polarimeter will form four simultaneous images of each star, enabling determinations of the magnitude, fractional polarization, and polarization angle for each object. It will be deployed on a 1-meter telescope at the South African Astronomical Observatory (SAAO). Combined with distance measurements from the GAIA spacecraft, the polarization data will enable 3D tomography of the interstellar medium, providing information that may enable scientists to extract the very weak polarization signal expected from the cosmic microwave background (CMB). The Intellectual Merit of the work derives primarily from the fact that improved mapping of the dust distribution in the Galaxy may enable astronomers to detect a predicted weak polarization signal (the so-called "B-mode" signal) in CMB radiation, significantly improving cosmologists' understanding of the very early Universe. The observations also will improve astronomers'understanding of dust formation, evolution, composition, and alignment by magnetic fields in the Galaxy. The investigators plan strong programs aimed at undergraduates, graduate students, and postdocs at Caltech, at IUCAA in India, at the SAAO, and at the University of Crete in Greece, combining instrument development with cutting-edge astrophysics and cosmology programs and including reciprocal visits among the partner institutions.