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会有非常微弱的偏振信号。然而，来自我们银河系星际云和磁场的更强信号阻止了科学家测量这个微弱的信号。恒星之间的空间包含许多这样的气体和尘埃云。戏剧性的天文图像揭示了它们--例如，猎户座中的大星云或著名的鹰星云。星际云中的尘埃颗粒也会使反射的星光产生微弱的偏振。天文学家可以测量这种微弱的偏振，以便找到星际云。在这个项目中，研究人员将建造一种新的仪器来测量星际尘埃云产生的光学偏振。利用这些测量和宇宙飞船的数据，他们将绘制出银河系云和磁场的位置。然后，科学家可以将他们的信号从宇宙微波背景辐射中分离出来。这个项目通过增加我们对早期宇宙的了解来服务于国家利益。研究人员将让一个由本科生、研究生和博士后组成的国际团队参与到这个项目的各个方面，给这个项目带来强大而广泛的影响。研究人员将设计和建造一台新型广域线性光学偏振仪(WALOP)，并将使用该仪器测量星际尘埃引起的偏振，并绘制银河系尘埃的分布图。在30x30角分钟的视场下，旋光仪将形成每颗恒星的四张同时图像，从而能够确定每个物体的星等、偏振分数和偏振角。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，偏振数据将使星际介质的3D断层成像成为可能，提供的信息可能使科学家能够从宇宙微波背景(CMB)提取预期的非常弱的偏振信号。这项工作的学术价值主要来自这样一个事实，即改进了对银河系尘埃分布的绘制，可能使天文学家能够在CMB辐射中探测到预测的弱偏振信号(所谓的“B模”信号)，从而显著提高宇宙学家对非常早期宇宙的理解。这些观测还将提高天文学家对银河系中尘埃的形成、演化、组成和磁场排列的理解。研究人员计划针对加州理工学院、印度IUCAA、SAAO和希腊克里特大学的本科生、研究生和博士后开展强有力的项目，将仪器开发与尖端的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.