Basis and Behavior of Cosmic Ray Feedback

当我们宇宙中的星系形成并度过它们的生命时，它们与周围环境交换物质和能量。星系风是这种物质和能量交换的关键组成部分。该项目旨在研究星系风的起源和传播，特别关注以接近光速的速度运动的粒子的作用。这样的粒子被称为宇宙射线。（事实上，这种来自我们银河系的宇宙射线每天都与我们每个人互动！）这个项目的主要成果将是改进和扩展星系风的模型(1)，它可以洞察星系风的本质，(2)可以被天文学家用来将星系和宇宙射线的特性与风的特性联系起来，(3)可以适应于先进的计算机模拟星系在其整个生命周期中是如何形成和变化的。该项目还将通过直接培训等离子体和计算物理方面的研究生和本科生，以及利用项目成果开发大学课程的教材，加强美国的科学劳动力。此外，调查人员还将制定一项新的公共宣传计划，即“公园里的太阳”，在麦迪逊和密尔沃基的城市公园里提供太阳观赏和参与性活动。从技术上讲，可以从许多类型的星系中探测到风。对星系形成和演化的模拟表明，恒星形成必须受到反馈过程的限制，而由恒星能量和动量输出驱动的星系风可能是这种反馈的关键部分。在各种星系环境中对宇宙射线的射电和伽马射线探测器极大地扩展了我们对宇宙射线特性和底层星系特性的认识。虽然宇宙射线只占恒星能量输出的一小部分，但它们在驱动星系风方面发挥着巨大的作用，因为它们具有高流动性、长冷却时间和通过等离子体波与背景的强耦合。这个项目将研究在各种星际环境中这种耦合的基础。这部分工作将解决宇宙射线是否有效地耦合到完全和弱电离流出，小尺度星际湍流如何影响动量和能量转移，以及极端条件包括高气体密度和弱磁场如何影响耦合。研究人员将根据少量参数创建一个多功能的外流模型网格，以帮助解释风的观测结果，并在星系模拟中实现它们。他们将以这项工作为基础，在星系形成和演化的协作高级数值模拟中改进宇宙射线的处理。

As galaxies in our Universe form and live out their lives, they exchange matter and energy with their surroundings. Galactic winds are a key component of this exchange of matter and energy. This project aims to study the initiation and propagation of galactic winds with particular focus on the role of particles moving at speeds near the speed of light. Such particles are known as cosmic rays. (In fact, such cosmic rays from our own Milky Way Galaxy interact with each of us every day!) The major outcome of this project will be improved and extended models of galactic winds (1) that build insight into the nature of galactic winds, (2) that can be used by astronomers to connect galaxy and cosmic ray properties with wind properties, and (3) that can be adapted to advanced computer simulations of how galaxies form and change throughout their lifetimes. This project will also strengthen the US science workforce by directly training graduate and undergraduate students in plasma and computational physics and by using the project results to develop teaching materials for university courses. In addition, the investigators will develop a new public outreach program, "The Sun in the Park," that will offer solar viewing and participatory exercises in urban parks in Madison and Milwaukee.More technically, winds are detected from galaxies of many types. Simulations of galaxy formation and evolution have shown that star formation must be limited by feedback processes and that galactic winds driven by stellar energy and momentum output may be a key part of this feedback. Radio and gamma-ray probes of cosmic rays in a variety of galactic environments have greatly extended our knowledge of cosmic ray properties and those of the underlying galaxies. Although cosmic rays account for a small fraction of the energy output from stars, they have an outsized role in driving galactic winds through their high mobility, long cooling times, and strong coupling to the background through plasma waves. This project will investigate the basis for this coupling in a variety of interstellar environments. This part of the work will address whether cosmic rays couple efficiently to both fully and weakly ionized outflows, how small scale interstellar turbulence affects momentum and energy transfer, and how extreme conditions including high gas densities and weak magnetic fields affect the coupling. The investigators will create a versatile grid of outflow models based on a small number of parameters to aid in interpreting observations of winds and implementing them in galaxy simulations. They will use this work as a basis for improved treatments of cosmic rays in collaborative advanced numerical simulations of galaxy formation and evolution.