New Roles for Polarimetry

AST-0204886希尔德布兰德过去几十年的发现表明，磁场影响星系中气体的结构和能量平衡；它们为气体层提供大量垂直支撑；它们传输能量并改变星际冲击的结构；它们加速和限制宇宙射线；它们强烈地影响云坍塌形成恒星。我们对这些场的大部分理解是通过观察沿视线方向磁性排列的尘埃颗粒的部分吸收引起的星光偏振，以及通过观察相对密集区域磁性排列的尘埃颗粒的偏振发射而获得的。虽然极化测量促进了我们对磁场的理解，但对结果的解释受到未知因素的限制。偏振取决于平均磁场从视线的倾斜；取决于磁场的湍流；取决于尘埃颗粒与局部磁场的对准程度；取决于尘埃颗粒的大小、形状和组成。该项目由芝加哥大学的罗杰·希尔德布兰德博士指导，旨在通过研究每个因素来扩大旋光测量的作用。由希尔德布兰德博士建造的芝加哥大学旋光仪在这些研究中发挥了重要作用，但光谱的其他部分越来越依赖互补观测。关于磁场倾斜度的工作结合了亚毫米波长偏振测量和离子和中性分子的线宽测量。在850到1300微米的波长范围内的观测将使用位于夏威夷莫纳克亚的詹姆斯·克莱克·麦克斯韦望远镜的潜水仪器进行。对微波前景的观测将依赖已经部署用于测量背景极化的DASI(南极)和MAP(空间飞行任务)仪器。***

AST-0204886HildebrandDiscoveries in the last few decades have shown that magnetic fields affect the structure and energy balance of gas in galaxies; that they provide substantial vertical support for the gas layer; that they transport energy and modify the structure of interstellar shocks; that they accelerate and confine cosmic rays; and that they strongly influence the collapse of clouds to form stars. Much of our understanding of these fields has been gained by observations of the polarization of starlight due to partial absorption in magnetically aligned grains along the line of sight, and by observations of polarized emission from magnetically aligned dust grains in relatively dense regions. Although the polarization measurements have advanced our understanding of magnetic fields, the interpretation of the results has been limited by unknown factors. The polarization depends on the inclination of the mean magnetic field from the line of sight; on the turbulence of the field; on the degree of alignment of the dust grains with the local field; and on the size, shape, and composition of the dust grains. This project, directed by Dr. Roger Hildebrand at the University of Chicago, addresses opportunities to expand the role of polarimetry by investigating each of the factors. The University of Chicago polarimeter, built by Dr. Hildebrand, has an important role in these investigations, but there is increasing reliance on complementary observations in other parts of the spectrum. The work on the magnetic field inclination combines submillimeter wavelength polarimetry with measurements of line widths for ionic and neutral molecules. Observations in the wavelength range from 850 to 1300 micron will be made with the instrument SCUBA at the James Clerk Maxwell telescope on Mauna Kea, Hawaii. Observations of the microwave foregroung will rely on the instruments DASI (at the South Pole) and MAP (space mission) which are already deployed for measurements of background polarization. ***