New Roles for Polarimetry

过去几十年的发现表明，磁场会影响星系中气体的结构和能量平衡；它们为气层提供了大量的垂直支撑；它们传输能量并改变星际冲击的结构；它们加速并限制了宇宙射线；它们强烈地影响着云的坍缩以形成恒星。我们对这些场的大部分理解是通过观测星光的偏振而获得的，这是由于沿着视线的磁排列颗粒部分吸收，以及通过观测相对密集区域的磁排列尘埃颗粒的偏振发射。虽然极化测量提高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。极化取决于平均磁场与视线的倾斜度；论场的乱流；尘粒与局地场的对准度以及尘埃颗粒的大小、形状和组成。这个项目由芝加哥大学的罗杰·希尔德布兰德博士指导，通过研究每一个因素来解决扩大偏振法作用的机会。由希尔德布兰德博士建造的芝加哥大学偏振计在这些研究中发挥了重要作用，但对光谱其他部分的补充观测的依赖越来越大。磁场倾角的研究结合了亚毫米波长偏振法和离子和中性分子的线宽测量。在夏威夷莫纳克亚山的詹姆斯·克拉克·麦克斯韦望远镜上的水肺仪器将在850到1300微米的波长范围内进行观测。对微波前景的观测将依赖于已经部署用于测量背景极化的DASI（在南极）和MAP（空间任务）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. ***