Radio Polarimetry as a New Probe of the Interstellar Medium

在一种被称为法拉第旋转的效应中，线性极化的无线电波在穿过磁化气体时以它的位置角度旋转。这种效应可以用来确定中间磁场的强度。这个项目由哈佛大学的Bryan Gaensler博士领导，致力于研究新的观测和分析技术，以研究微弱的背景偏振，并测量由此产生的法拉第旋转。星际气体的磁性可以在广阔的天空区域进行测量，从而使人们能够在不可见的磁场中绘制出有序和湍流的结构。这些测量结果将被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。这些数据将用于描述星际弥漫气体和特定来源的磁湍流的强度和规模。星际湍流的性质如何随着位置的变化而变化，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到星际介质中，这些都可以确定。利用前景源中的法拉第旋转可以去极化极化的背景发射这一事实，还可以确定离散前景对象中的气体密度、磁场强度和湍流程度。在这个项目中，这一现象将用于测量HII区域湍流漩涡的规模，追踪超新星残余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，极化数据将用于确定银河系和麦哲伦星云的整体磁场结构。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，人们可以确定星系磁力是如何产生的。该项目的总体目标是全面了解磁场在整个空间中的分布情况，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个物体的能量学和动力学的基本贡献经常被忽视-这个项目应该改变这种情况。对于所有年龄层的外行人来说，要理解测量来自太空的无线电发射意味着什么，以及理解进行这些测量的过程，都是一项挑战。因此，作为上述科学计划的补充，将开展一些活动，其目的是使中学生和高中生能够了解这个项目背后的一些天体物理学主题。具体来说，将设计一些活动来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他们的数据，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，在更多的教室中进行改进和实地测试，然后通过WWW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.***