Origin and evolution of cosmic magnetism

观测表明，磁场在宇宙中无处不在。与重力一起，宇宙磁场指导着等离子体和宇宙射线的流动，并间接地指导着中性气体的运动。尽管如此，我们仍然无法回答关于宇宙磁场的结构、星系中大尺度磁场的起源以及太空中磁化等离子体中湍流的性质等基本问题。我们对宇宙磁场缺乏了解，在星系演化的物理学上留下了重大空白，从热气体和宇宙射线在盘中的保留，到支持冷分子云抵御引力崩塌。星系代表着宇宙中可见的结构部分。正是在这里，恒星的核合成建立了氢、氦和锂以外的元素。经过近140亿年的演化，所有可观测到的气体似乎都富含恒星核合成的产物，即使在星际空间也是如此。这一事实证明了银河系尺度上恒星的生命周期对星系及其广泛环境的演化产生的影响。一些星系还拥有活动星系核(AGN)，活动星系核由中心超大质量黑洞上的物质吸积提供动力。被称为喷流的物质束以大量相对论速度喷射，并在比星系大得多的星际空间中形成巨大的磁射电叶。恒星和活动星系核对物质的喷射及其相关的动能和动量被称为恒星反馈和活动星系核反馈。如果没有反馈的物理学，我们就无法理解星系的演化。磁场在反馈物理学中扮演着重要的角色，例如在恒星形成、宇宙射线的加速和扩散、限制星系外流和准直喷流的各个阶段。反过来，恒星反馈为发电机效应提供能量，从而放大磁场，而来自活动星系核的流出和喷射可以向星系间介质注入磁场。揭示磁场的结构和动力学重要性的观测为反馈和湍流模型提供了至关重要的指导。这项研究计划的目标是星系中气体和磁场之间的复杂反馈过程，以及它们与宇宙磁场出现的关系。在接下来的五年里，我们将通过测量本星际介质中等离子体和中性气体的速度，以及从能量注入尺度到最小可见湍流的磁场测量来引领这一趋势。我们将解决螺旋星系和射电星系叶中的磁场如何随着宇宙时间的推移而演变的问题--这是恒星和活动星系核反馈的主要地点。我的团队擅长堆叠、星系的综合极化和自转测量的统计。我们将通过根据调查政策提出的明确的科学项目来引导这些技术的应用，以实现我们的目标。

Observations show that magnetic fields are ubiquitous in the cosmos. Together with gravity, cosmic magnetic fields direct the flow of plasma and cosmic rays, and, indirectly, the motion of neutral gas. Still, we cannot answer basic questions about the structure of cosmic magnetic fields, the origin of large-scale magnetic fields in galaxies, and the properties of turbulence in magnetized plasma in space. Our lack of understanding of cosmic magnetic fields leaves major gaps in the physics of galaxy evolution, from the retention of hot gas and cosmic rays in the disk to support of cold molecular clouds against gravitational collapse. Galaxies represent the visible part of structure in the universe. It is here that stellar nucleosynthesis builds elements beyond hydrogen, helium and lithium. After nearly 14 billion years of evolution, all observable gas appears enriched by the products of stellar nucleosynthesis, even in intergalactic space. This fact bears testimony to the impact that the life cycle of stars on a galactic scale has on the evolution of galaxies and their wide environment. Some galaxies also host active galactic nuclei (AGN), that are powered by accretion of matter on a central, supermassive black hole. Beams of matter called jets are ejected at bulk relativistic speed, and form giant magnetic radio lobes in intergalactic space much larger than a galaxy. The ejection of matter, and its its associated kinetic energy and momentum, by stars and AGN is referred to as stellar feedback and AGN feedback. We cannot understand galaxy evolution without the physics of feedback. Magnetic fields play an important role in the physics of feedback, for example during various stages of star formation, acceleration and diffusion of cosmic rays, constraining galactic outflows, and collimating jets. In turn, stellar feedback provides energy for dynamo effects that amplify magnetic fields, while outflows and jets from AGN can inject magnetic fields into the intergalactic medium. Observations that reveal the structure an dynamical importance of magnetic fields provide crucial guidance for models of feedback and turbulence. This research program targets the complex feedback processes between gas and magnetic fields in galaxies, and their relation to the emergence of cosmic magnetic fields. In the next five years, we will lead by combining measurements of the velocity of plasma and neutral gas in the local interstellar medium with measurements of the magnetic field from the energy injection scale to the smallest observable turbulence. We will address the question of how magnetic fields evolved over cosmic time in spiral galaxies and in the lobes of radio galaxies - the main sites for stellar and AGN feedback. My group excels in stacking, integrated polarization of galaxies, and statistics of rotation measures. We will lead application of these techniques toward our objectives through defined science projects proposed according to survey policies.