The Role of Cosmic Magnetic Fields in Galaxy Evolution

磁场在银河系形成中的作用地球磁场保护我们的大气层免受太阳风的冲击，太阳风是一股从太阳流经太阳系的等离子体流。太阳磁场的扰动可能会引发物质大规模抛射到太空中，当物质与地球磁场相互作用时，可能会导致电力中断，GPS设备和卫星通信中断。最近，NASA的旅行者1号太空探测器记录到了磁场强度的突然变化，但方向没有变化，因为它可能进入了星际空间。磁场弥漫整个宇宙。在许多天体物理情况下，从小到大，磁场在宇宙中的物质运动中起着决定性的作用。反过来，宇宙磁场的结构与物质的运动密切相关。了解磁场对于了解结构的形成和随后的演化是必要的。在这个提议中，我概述了一个研究计划，该计划研究与星系形成和演化有关的磁场物理。这包括通过物质的吸积来组装星系，但也包括磁场和星系内物质之间的相互作用，以及星系中心的活动(活动星系核或AGN)以物质束的形式向星际空间喷射大量能量。目前，我们对星系中的磁场知之甚少。这在一定程度上是由于发电机理论的预测性质的局限性，该理论描述了如何通过天体物理等离子体中的运动来放大和维持大范围的磁场。在某种程度上，我们对宇宙磁场缺乏了解是因为我们从观测中获得定量信息的能力有限。后者将在下一个十年向前迈出重要的一步，因为接收器技术的最新发展，以及一个新的国际射电天文设施的设计，称为平方公里阵列(SKA)。SKA的五个关键科学目标之一是研究宇宙磁性的起源和演化，另一个目标包括星系演化和宇宙学。对于正常星系，我研究了磁场与诸如恒星形成速率和星系动力学等全球性质的关系。为此，我领导了埃菲尔斯伯格射电望远镜和扩展甚大天线阵(EVLA)的调查。在我们银河系小得多的尺度上，我研究了气体和小尺度磁场之间的联系。我领导了一项对部分银河系圆盘(雷神)的调查，以及使用阿雷西博300米射电望远镜进行GALFACTS调查的早期科学项目的偏振方面的工作。通过合作对天空小区域进行深度调查，我们调查了遥远星系和活动星系核供电的射电源的性质。射电星系的磁场特性也是使用一种名为堆叠的技术进行的统计调查的主题，这是GALFACTS调查的另一个早期科学项目。这项工作包括使用最先进的设施进行观测，以及对无线电发射和磁场进行建模。为了支持未来用SKA及其探路器进行天空测量的发展，我还在研究从无线电波极化的宽带观测中提取信息的新应用，无线电波极化是有关宇宙磁场的主要信息来源。这将使我们更深入地了解宇宙中磁场的起源，以及它们在宇宙结构形成中的作用。

The Role of Magnetic Fields in Galaxy Formation Earth's magnetic field protects our atmosphere from the onslaught of the solar wind: a stream of plasma flowing from the Sun through the Solar System. A disturbance in the Sun's magnetic field can trigger a massive ejection of matter into space that can cause power outages and disruption of GPS equipment and satellite communication when it interacts with the Earth's magnetic field. Recently, NASA's Voyager 1 space probe recorded a sudden change in magnetic field strength, but not direction, as it presumably entered interstellar space. Magnetic fields pervade the universe. In many astrophysical situations from small to very large, magnetic fields play a decisive part in the motion of matter in the cosmos. In return the structure of cosmic magnetic fields is intimately related to the motion of matter. Understanding magnetic fields is necessary to understand the formation of structure, and its subsequent evolution. In this proposal I outline a research program that investigates the physics of magnetic fields in relation to the formation and evolution of galaxies. This includes galaxy assembly by accretion of matter, but also the interaction between magnetic fields and matter inside galaxies, and activity in the centre of galaxies (Active Galactic Nucleus or AGN) that ejects vast amounts of energy in the form of beams of matter into intergalactic space. For the moment, we know very little with confidence about magnetic fields in galaxies. This is in part due to limitations in the predictive nature of dynamo theory that describes how large-scale magnetic fields can be amplified and sustained from motions in an astrophysical plasma. In part, our lack of understanding of cosmic magnetic fields is due to limitations in our ability to derive quantitative information from observations. The latter will make significant steps forward in the next decade because of recent developments in receiver technology, and the design of a new international facility for radio astronomy called the Square Kilometre Array (SKA). One of five key science goals for the SKA is to study the origin and evolution of cosmic magnetism, and another includes galaxy evolution and cosmology. For normal galaxies, I investigate the relation of the magnetic field to global properties such as the rate of star formation and dynamics of a galaxy. To this end, I lead surveys with the Effelsberg radio telescope and the Expanded Very Large Array (EVLA). On much smaller scales in our own Milky Way galaxy, I investigate the connection between the gas and the small-scale magnetic field. I lead the polarization side of a survey of part of the disk of the Milky Way (THOR), and an early science project of the GALFACTS survey with the Arecibo 300-m radio telescope. Through collaboration on deep surveys of small areas of the sky, we investigate the properties of distant galaxies and AGN-powered radio sources. The magnetic field properties of radio galaxies are also the subject of a statistical investigation using a technique called stacking, and another early science project with the GALFACTS survey. This work includes both observations with state of the art facilities and modeling of radio emission and magnetic fields. In support of development of future sky surveys with SKA and its path finders, I am also investigating new applications to extract information from broad-band observations of the polarization of radio waves, the principal source of information about cosmic magnetic fields. This will lead to a deeper understanding of the origin of magnetic fields in the cosmos, and their role in the formation of structure in the universe.