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，宇宙磁场引导等离子体和宇宙射线的流动，并间接引导中性气体的运动。尽管如此，我们仍然无法回答关于宇宙磁场结构、星系中大尺度磁场的起源以及空间磁化等离子体湍流性质的基本问题。我们对宇宙磁场的缺乏了解，在星系演化的物理学中留下了重大的空白，从盘中热气体和宇宙射线的保留到冷分子云对引力坍缩的支持。星系代表宇宙中可见的部分结构。正是在这里，恒星核合成产生了氢、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，即使在星系际空间也是如此。这一事实证明了恒星在星系尺度上的生命周期对星系演化及其广泛环境的影响。一些星系也拥有活动星系核（AGN），这些活动星系核由中央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整体相对论速度喷出，并在星系际空间形成比星系大得多的巨大磁射电瓣。恒星和活动星系核对物质的喷射，以及与之相关的动能和动量，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，例如在星星形成的各个阶段，宇宙射线的加速和扩散，限制银河系外流和准直喷流。反过来，恒星反馈为发电机效应提供能量，放大磁场，而AGN的流出物和喷流可以将磁场注入星系际介质。揭示磁场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。该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，我们将通过将局部星际介质中等离子体和中性气体速度的测量与从能量注入尺度到最小可观测湍流的磁场测量相结合来领导。我们将讨论在旋涡星系和射电星系的叶中磁场是如何随宇宙时间演化的问题--这些叶是恒星和活动星系核反馈的主要场所。我的团队擅长于叠加，星系的综合偏振，以及旋转测量的统计。我们将通过根据调查政策提出的明确的科学项目，引导这些技术的应用实现我们的目标。

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.