Radio Polarimetry as a New Probe of the Interstellar Medium

AST 0307358 Gaensler在一种被称为法拉第旋转的效应中，线性偏振的无线电波在穿过磁化气体时以其位置角旋转。这种效应可以用来确定干扰磁场的强度。该项目由哈佛大学的Bryan Gaensler博士领导，追求新的观测和分析技术，用于研究微弱的背景偏振，并测量随之而来的法拉第旋转。然后，星际气体的磁性可以在天空的广阔区域内测量，使人们能够在其他不可见的磁场中绘制出有序和湍流结构。 这些测量将应用于我们自己的银河系和离我们最近的两个星系，大麦哲伦云和小麦哲伦云的拓扑极化数据。这些数据将被用来表征磁湍流的强度和规模，无论是在弥漫的星际气体和对特定的来源。星际湍流的性质如何随位置而变化，在一定的物理尺度上是否存在从三维到二维的湍流过渡，以及湍流是否在特定的位置注入星际介质，都可以由此确定。利用前景源中的法拉第旋转可以消除偏振背景发射的事实，还可以确定离散前景物体内的气体密度、磁场强度和湍流程度。在该项目中，这一现象将被用来测量HII区域湍流涡旋的尺度，追踪超新星遗迹激波产生的增强湍流，并探测年轻恒星与分子云之间的相互作用。最后，偏振数据将用于确定银河系和麦哲伦云的整体磁场结构。利用这些磁场的几何形状以及它们与星际气体分布的关系，人们可以确定银河系磁性是如何产生的。该项目的总体目标是全面了解磁场如何在整个空间中分布，从与随机运动和湍流相关的小尺度到全球银河系结构。磁场对我们银河系及其内每一个物体的能量学和动力学的基本贡献常常被忽视--这个项目应该改变这种情况。对于所有年龄段的外行人来说，理解测量来自太空的无线电辐射意味着什么，理解这些测量的过程是具有挑战性的。因此，作为对上述科学方案的补充，将开展一些活动，其目的是使初中和高中学生了解该项目所依据的一些天体物理学主题。具体而言，将设计的活动将证明无线电波是电磁辐射的一种形式，解释射电天文学家如何收集数据，强调避免和克服无线电频率干扰的必要性，并解释干涉测量的基本原理。这些活动将在当地学校进行试点，评估学生的参与和理解水平，在更多的教室进行改进和实地测试，然后通过万维网免费提供。

AST 0307358GaenslerIn an effect known as Faraday rotation, a linearly polarized radio wave rotates in its position angle as it travels through a magnetized gas. This effect can be used to determine the strength of the intervening magnetic field. This project, led by Dr. Bryan Gaensler at Harvard University, pursues new observing and analysis techniques for studying faint background polarization, and for measuring the consequent Faraday rotation. The magnetic properties of interstellar gas can then be measured over wide regions of the sky, allowing one to map out both ordered and turbulent structures in otherwise invisible magnetic fields. These measurements will be applied topolarization data on both our own Milky Way and on the two nearest galaxies to our own,the Large and Small Magellanic Clouds. These data will be used to characterize the strength and scale of magnetic turbulence, both in diffuse interstellar gas and towards specific sources. How the properties of interstellar turbulence vary as a function of location, whether there is a transition from three- to two dimensional turbulence at a certain physical scale, and if turbulence is injected into theinterstellar medium at particular sites, can all thus be determined. Using the fact that Faraday rotation in foreground sources can depolarize polarized background emission, one can also determine the gas density, magnetic field strength and degree of turbulence within discrete foreground objects. In this project, this phenomenon will be used to measure the scale of turbulent eddies in HII regions, to trace out the enhanced turbulence produced by supernova remnant shocks, and to probe the interaction between young stars and molecular clouds. Finally, polarization data will be used to determine the overall magnetic field structure of the Milky Way and of the Magellanic Clouds. Using the geometry of these fields and their relation to the distribution of interstellar gas, one can determine how galactic magnetism is generated. The overall goal of this project is to reach a full understanding of how magnetic fields are distributed throughout space, ranging from the small scales associated with random motions and turbulence, up to global Galactic structure. The fundamental contribution made by magnetic fields to the energetics and dynamics of our Galaxy and of every object within it are often overlooked - this project should amend this situation.It is challenging for lay people of all ages to understand just what it means to measure the radio emission from space, and to comprehend the process through which these measurements are carried out. As a complement to the scientific program described above, activities will therefore be developed whose aim will be to make some of the astrophysical themes underlying this project accessible to middle- and high-school students. Specifically, activities will be designed which demonstrate that radio waves are a form of electromagnetic radiation, which explain how radio astronomers gather their data, which highlight the need to avoid and overcome radio frequency interference, and which explain the principles underlying interferometry. These activities will be piloted in local schools, assessed for their levels of student engagement and comprehension, refined and field-tested in a larger number of classrooms, and then made freely available via the WWW.***