Collaborative Research: Cosmic Ray Feedback from Plasma to Circumgalactic Scales

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The self-regulation of star formation through feedback, the launching of galactic winds, and the interactions between galaxies and their circum-galactic medium, are fundamental and interrelated components of galaxy formation and evolution. The primary agents of feedback are the thermal and turbulent energy of interstellar gas, radiation, and magnetized cosmic rays. Cosmic rays exchange momentum and energy with the background medium and may be better coupled to the ionized gas than are the photons, but the physical and computational tools needed to include them in galaxy models are still at an early stage, and have not yet been fully studied. This project addresses this “cosmic ray gap” by developing and implementing new tools for studying the plasma physics of cosmic rays as it applies to star formation feedback. The team will organize outreach events to improve general scientific literacy, including planetarium shows and public lecture series. Undergraduates and graduate students will be involved in all aspects of the research, providing broad professional training. Workshops will foster collaborations among participants who share closely related interests in the physics of cosmic rays, magnetic fields, and interstellar and intra-cluster feedback.The collaborators have complementary and overlapping expertise in plasma astrophysics theory, computational astrophysics, cosmic ray physics, and the astrophysics of galaxy evolution. This study will cover processes on length scales from the sub-AU microscopic plasma scales to the 100 kpc circum-galactic scales, and will combine state of the art fluid dynamical and hybrid fluid–kinetic numerical simulations with analytical theory. The research goals include: (1) find improved prescriptions for including cosmic rays in models of stellar feedback; (2) quantify an “Eddington Limit” for the cosmic ray flux necessary to unbind the interstellar gas in a galaxy; (3) construct models of the circum-galactic medium that include cosmic rays; (4) make predictions for observational tests of the role of cosmic rays. For comparison with data, the investigators will calculate the non-thermal gamma-ray and radio synchrotron emission from models with cosmic rays; the gamma-ray results will be used to interpret observations with Fermi.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.