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

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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.