From Galactic Centers to Galactic Fringes: Control of Star Formation in the Dynamic Interstellar Medium

越来越多的观测正在探索盘状星系中星星形成率和局部条件之间的关系，但确定这些速率的机制还没有得到很好的理解。特别是，虽然人们普遍认为，能量反馈自我调节星星的形成，这个过程的详细模型尚未开发。巨分子云中的H II区和超新星都可以触发星星的形成和截断（通过云的破坏），反馈驱动的扩散星际介质（ISM）湍流可以促进和抑制新的GMC的创建。控制星星形成的其他因素包括：气体自重，它将ISM聚集成巨大的云;恒星成分的重力，它垂直地限制ISM;加热和冷却过程，它将ISM分成密集和分散的热相;剪切轨道旋转和科里奥利力，它抑制收敛流;和磁场，它介导角动量交换。Eve Ostriker博士（马里兰州大学帕克分校）和合作者将研究这些过程如何相互作用以调节大规模星星的形成，确定主导效应并根据常见的观测数据进行定量预测。这项研究将涉及一系列集中的数值模拟，分别针对星星形成的三个区域：星系中心，中间盘和外部盘。 将采取的方法与最近的其他数值工作不同，因为模拟将集中在局部（1至1000秒差距）而不是全球（30至30 000秒差距）尺度，直接遵循星系演化模型中经常使用次网格规定处理的过程。每个模拟域将足够大，以捕捉重要的银河系环境的影响，但足够小，使湍流和密度结构的气体是很好地解决了数值网格。初步研究表明，ISM盘的垂直分辨率对于正确估计星星形成的表面密度至关重要。预计这项工作将对劳动力、教育和研究基础设施产生更广泛的影响。 它们包括（1）培训和指导学生，包括一名从事建模和分析的博士生，以及Ostriker博士在相关观测和科学计算项目中提供建议的其他研究生（共同），（2）将科学研究成果和计算模块整合到本科和研究生课程的教学课程中。(3)面向公众的外联活动，包括创建视觉效果丰富的网页和在开放日活动中进行演示，以及（4）开发、实施和测试计算流体力学/磁流体力学模拟的新工具，作为既定代码包的一部分与社区共享。

Observations are increasingly probing the relationship between star formation rates and local conditions in disk galaxies, but the mechanisms that set these rates are not well understood. In particular, while it is widely believed that energetic feedback self-regulates star formation, detailed models of this process have not yet been developed. H II regions and supernovae in giant molecular clouds (GMCs) can both trigger star formation and truncate it (by cloud destruction), and feedback-driven diffuse-interstellar medium (ISM) turbulence can both enhance and suppress the creation of new GMCs. Additional elements that control star formation include: gas self-gravity, which gathers the ISM into massive clouds; the stellar component's gravity, which confines the ISM vertically; heating and cooling processes, which separate the ISM into dense and diffuse thermal phases; sheared orbital rotation and Coriolis forces, which suppress converging flows; and magnetic fields, which mediate angular momentum exchange. Dr. Eve Ostriker (University of Maryland College Park) and collaborators will study how these processes interact to regulate large-scale star formation, identifying the dominant effects and developing quantitative predictions in terms of common observables. The research will involve a series of focused numerical simulations, separately targeting three regimes of star formation: galactic center, mid-disk, and outer disk. The approach to be taken is distinct from other recent numerical work in that the simulations will concentrate on local (1 to 1000 parsec) rather than global (30 to 30,000 parsec) scales, directly following processes that are often treated using sub-grid prescriptions in galaxy evolution models. Each simulation domain will be large enough to capture the important galactic environmental effects, but small enough so that the turbulence and density structure of the gas is well resolved by the numerical grid. Preliminary studies have shown that vertical resolution of the ISM disk is crucial to correctly estimating the surface density of star formation.It is expected that this work will have broader impacts on workforce, education, and research infrastructure. They include (1) training and mentoring of students, including a PhD student working on modeling and analysis, and additional graduate students (co-)advised by Dr. Ostriker in related observational and scientific computation projects, (2) integration of scientific research results and computational modules in instructional curricula for undergraduate and graduate courses. (3) outreach activities for the public, including creation of visually-rich web pages and presentations at open house events, and (4) development, implementation, and testing of new tools for computational hydrodynamics/magneto-hydrodynamic simulation, to be shared with the community as part of an established code package.