Star Formation, ISM, and Winds in Bursty vs. Steady Galaxies

Northwestern University, Evanston IL

Investigators

Abstract

Stars form in galaxies wherever molecular gas becomes sufficiently cold and dense to become gravitationally unstable, which initiates fragmentation and subsequent collapse. Once formed, however, stars can profoundly affect their surroundings through the energy injected by supernovae, ultraviolet radiation, and fast stellar winds, processes collectively referred to as "stellar feedback." Stellar feedback can suppress the star formation rate (SFR), regulate the overall mass growth of a galaxy, and shape its multi-phase interstellar medium (ISM). While there has been much progress in modeling stellar feedback, previous work has focused primarily on Milky Way-like systems, where the SFR is fairly constant. However, star formation in low-mass and/or high-redshift galaxies tend to have highly episodic or "bursty" SFRs, where stellar feedback may work in fundamentally different ways relative to local spirals. The principal investigator and team will extend stellar feedback theory from "steady" systems to bursty ones, and in particular, the small and highly gas rich examples recently found at high-redshift that are likely the progenitors of Milky Way-like systems, and which are the focus of many observational studies by state-of-the-art ground- based and space-based observatories. In addition to a postdoc, this award will support the mentoring of three undergraduate researchers, outreach events at Chicago's Adler Planetarium and other public events, and improvements in FIREFLY, an interactive scientific visualization tool. The proposed research will be centered on a large suite of zoom-in simulations that resolve the ISM of individual galaxies in a cosmological context, and which self-consistently model the transition from bursty to steady galaxies. The simulations include all the main forms of stellar found in galaxies from dwarfs to super-L*. The project will focus on three core science issues: (1) the applicability of “equilibrium disk” or “pressure balance” models for the origin of the Kennicutt-Schmidt star formation law, (2) the dynamical and thermodynamic properties of the ISM and its relationship to the circumgalactic medium, and (3) the launching of galactic winds and galactic fountains in bursty vs. steady galaxies. Variants of the simulations will include additional physical processes (e.g., magnetic fields, cosmic rays, and non-equilibrium ISM chemistry) to test how the results depend on these additional variables. Observational predictions will be made to test the simulation predictions in the different regimes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.