Radio Polarimetry as a New Probe of the Interstellar Medium

射电偏振测量作为星际介质的新探测器

• 批准号: 0307358
• 负责人: Charles Alcock
• 金额: $ 33.68万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0307358&HistoricalAwards=false
• 关键词: Radio; Polarimetry; New; Probe; Interstellar

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.***

AST0307358 Gaensler在一种称为法拉第旋转的效应中，线偏振无线电波在通过磁化气体时会以其位置角旋转。这一效应可以用来确定插入磁场的强度。该项目由哈佛大学的布莱恩·甘斯勒博士领导，致力于探索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。然后，星际气体的磁特性可以在天空的大范围内进行测量，从而可以绘制出在其他看不见的磁场中的有序和湍流结构。这些测量将在我们自己的银河系和距离我们最近的两个星系--大麦哲伦云和小麦哲伦云--上应用拓扑化数据。这些数据将被用来描述弥漫星际气体中和朝向特定来源的磁湍流的强度和规模。因此，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湍流到二维湍流的转变，以及是否在特定位置将湍流注入星际介质，都可以确定。利用前景源中的法拉第旋转可以去极化背景辐射的事实，还可以确定离散前景对象内的气体密度、磁场强度和湍流程度。在这个项目中，这一现象将被用来测量HII区的湍流涡度，追踪超新星遗迹激波产生的增强湍流，并探索年轻恒星与分子云之间的相互作用。最后，极化数据将被用来确定银河系和麦哲伦星云的总体磁场结构。利用这些磁场的几何形状及其与星际气体分布的关系，可以确定银河系的磁性是如何产生的。该项目的总体目标是全面了解磁场是如何在整个空间分布的，范围从与随机运动和湍流有关的小尺度到全球银河系结构。磁场对我们银河系和银河系内每个物体的能量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。对于所有年龄段的外行来说，理解测量来自太空的射电辐射到底意味着什么，并理解进行这些测量的过程是具有挑战性的。因此，作为上述科学计划的补充，将开展一些活动，其目的是使初中生和高中生能够接触到这一项目所涉及的一些天体物理学主题。具体而言，将设计一些活动，说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，突出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试行，评估学生的参与度和理解力水平，在更多的教室进行改进和实地测试，然后通过WWW免费提供。