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恒星形成速率与当地条件之间的关系，但设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可以自我调节恒星形成，但这一过程的详细模型尚未开发出来。巨分子云（GMCs）中的H II区域和超新星既可以触发恒星形成，也可以（通过云破坏）截断它，反馈驱动的漫射星际介质（ISM）湍流既可以增强也可以抑制新GMCs的产生。控制恒星形成的其他因素包括：气体自引力，它将ISM聚集成巨大的云；恒星部分的重力，它在垂直方向上限制了ISM；加热和冷却过程，将ISM分为密集和扩散热相；剪切轨道旋转和科里奥利力，抑制汇聚流；还有磁场，它调节角动量交换。Eve Ostriker博士（马里兰大学帕克分校）及其合作者将研究这些过程如何相互作用以调节大规模恒星形成，确定主要影响并根据常见观测结果进行定量预测。这项研究将包括一系列集中的数值模拟，分别针对三种恒星形成机制：星系中心、中盘和外盘。采用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）而不是全局（30至30,000秒差距）尺度上，直接遵循星系演化模型中经常使用子网格处方处理的过程。每个模拟域都足够大，以捕捉重要的星系环境效应，但又足够小，以便通过数值网格很好地解决气体的湍流和密度结构。初步研究表明，ISM盘的垂直分辨率对于正确估计恒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，以及由Ostriker博士指导的其他研究生（共同）从事相关的观测和科学计算项目；(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)面向公众的外展活动，包括创建视觉丰富的网页和在开放日活动上的演讲；(4)开发、实施和测试计算流体动力学/磁流体动力学模拟的新工具，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.