The Role of Cosmic Magnetic Fields in Galaxy Evolution

磁场在星系形成中的作用**地球的磁场保护我们的大气层免受太阳风的冲击。太阳风是一种从太阳流过太阳系的等离子体流。太阳磁场的扰动会引发大量物质喷射到太空中，当它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，美国宇航局的旅行者1号太空探测器记录到磁场强度的突然变化，但没有方向，因为它可能进入了星际空间。磁场遍布宇宙。在许多从小到非常大的天体物理情况下，磁场在宇宙中物质的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。理解磁场对于理解结构的形成及其随后的演化是必要的。**在这个建议中，我概述了一个研究计划，该计划调查磁场物理学与星系形成和演化的关系。这包括通过物质吸积形成的星系，也包括星系内部磁场和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系间空间喷射大量能量。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特性的局限性，发电机理论描述了如何从天体物理等离子体的运动中放大和维持大规模的磁场。在某种程度上，我们对宇宙磁场缺乏了解是由于我们从观测中获得定量信息的能力有限。由于接收器技术的最新发展，以及一种新的国际射电天文学设施——平方公里阵列（SKA）的设计，后者将在未来十年取得重大进展。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，另一个包括星系演化和宇宙学。**对于正常星系，我研究了磁场与整体特性的关系，如恒星形成速率和星系动力学。为此，我领导了Effelsberg射电望远镜和扩展甚大阵列（EVLA）的调查。在我们银河系更小的尺度上，我研究了气体和小尺度磁场之间的联系。我领导了对银河系部分圆盘（THOR）的偏振调查，以及用阿雷西博300米射电望远镜进行GALFACTS调查的早期科学项目。通过对天空小区域的深入调查，我们研究了遥远星系和agn供电的射电源的特性。射电星系的磁场特性也是利用一种叫做叠加的技术进行统计调查的主题，也是GALFACTS调查的另一个早期科学项目。**这项工作包括用最先进的设备进行观测和无线电发射和磁场的建模。为了支持未来用SKA及其寻径器进行天空调查的发展，我也在研究从无线电波偏振的宽带观测中提取信息的新应用，无线电波偏振是宇宙磁场信息的主要来源。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.