Collaborative research: Multiscale physics and feedback in real and simulated circumgalactic gas over cosmic time

尽管科学家们对宇宙中的星系了解甚多，但对环绕它们的气体知之甚少，尤其是对这些物质储存库与望远镜图像中如此熟悉的视觉上令人惊叹的区域之间的相互作用知之甚少。这项真正独特的研究涵盖了物理尺度上的巨大范围，从最小的可观测云到星系团，以展示可见星系与其周围环境之间的真实动态相互作用。初级研究人员和学生将学习如何运行和解释最先进的数值模拟，以及如何对现有的观测档案进行数据挖掘。环星系介质（CGM）是星系周围弥漫的气体，充当着燃料箱、垃圾场和回收中心的角色。最近的发现表明，CGM是动态的，快速演化的，具有显著的质量，并在决定星系的质量，形状和恒星形成特性方面起着关键作用。本项目采用数据与模型相结合的新方法，在物理尺度上考察CGM在星系演化中的作用，这是真正了解其条件和运动学所必需的。数据将从现有档案中挖掘，模型将来自一套最先进的数值模拟。严格的比较将使用该团队开发的工具包，从模拟中生成模拟数据集，然后可以将其与真实数据相结合进行分析。这项工作将解决几个难题：1)虽然化学元素丰富，但致密的CGM并不像预测的那样混合良好；2)星系中有大量富含金属的气体，冷却时间应该非常短；3)冷的CGM过于分散，无法与热的星系日冕达到压力平衡；4)在被动星系的CGM中有和恒星形成星系一样多的冷中性气体，因此这些气体既不是恒星形成的燃料，也不是恒星形成的副产品。这种理解只能通过在观测可以探测到的最小单个云的尺度上理解物理学的突破来获得，这是不可能的，除非使用与数据严格耦合的多尺度模拟。这项研究将揭示CGM气体的物理状态，限制CGM云演化的时间尺度，并确定进出星系的质量流率和总质量。这些结果将成为所有团队成员向不同机构周围地区的不同社区进行外展会谈的重点。该项目将让初级科学家参与一线研究，特别是针对代表性不足的学生，并为中级研究人员的指导技能做出贡献。它还将支持开发一个新的天文馆展览，其中包括星系中气体的可视化流体动力学模拟。

Although scientists know a great deal about galaxies in the Universe, less is known about the gas that surrounds them all and especially about the interplay between this reservoir of material and the visually stunning regions so familiar from telescope images. This truly unique study covers an enormous range in physical scale, from the smallest observable clouds to clusters of galaxies, to show the real dynamical interaction between the visible galaxies and their surroundings. Junior researchers and students will learn how to run and to interpret state-of-the-art numerical simulations, and how to carry out data mining on existing observation archives.The circum-galactic medium (CGM) is the diffuse gas surrounding galaxies that acts as a fuel tank, waste dump, and recycling center. Recent discoveries show that the CGM is dynamic, rapidly evolving, has significant mass, and plays a key role in determining the mass, shape, and star-forming properties of galaxies. This project applies a new combination of data with models to examine the role of the CGM in galaxy evolution over seven orders of magnitude in physical scale, which is required to truly understand its conditions and kinematics. The data will be mined from existing archives, and the models will come from a suite of state-of-the-art numerical simulations. The rigorous comparison will use a toolkit developed by this team to produce mock datasets from simulations, which can then be analyzed in concert with the real data. This work should solve several puzzles: 1) although abundant in chemical elements, the dense CGM is not as well-mixed as predicted; 2) galaxies have massive reservoirs of metal-rich gas that should have an extremely short cooling time; 3) the cool CGM is too diffuse to be in pressure equilibrium with a hot galactic corona; and 4) there is just as much cool, neutral gas in the CGM of passive galaxies as in that of star-forming galaxies, so that this gas can be neither fuel for, nor a by-product of, star formation. This understanding can only be gained by a breakthrough in understanding physics at the scales of the smallest individual clouds that observations can detect, which is not possible except by using multi-scale simulations rigorously coupled to data. The study will reveal the physical state of CGM gas, constrain the timescales over which CGM clouds evolve, and determine the mass flow rates and total masses moving in and out of galaxies.These results will be the focus of outreach talks by all team members to the diverse communities in the areas around the different institutions involved. The project will involve junior scientists in front line research, especially targeting under-represented students, and contributing to mentoring skills amongst the intermediate-level researchers. It will also support development of a new planetarium show that includes visualized hydro-dynamical simulations of the gas in galaxies.