The impact of cosmic rays on the interstellar medium

Cosmic rays (CRs) are a fundamental ingredient in the structure and evolution of galaxies. Mostly produced within galactic disks through shock acceleration in supernova, these high-energy non-thermal particles easily spread throughout the interstellar medium (ISM). Evidence suggests that CRs may significantly contribute to the dynamics of the ISM, and understanding how CRs impact ISM dynamics on galactic scales is central to galaxy evolution studies.

This research team will carry out a comprehensive theoretical investigation of how the distribution of CRs, in space and energy, vary with the dynamical, thermal, and magnetic properties of the gas. The investigators will train and mentor a graduate student and an undergraduate student for PhD dissertation and senior thesis research, respectively. The team will make the visual materials from the simulations public and easily accessible through the creation of a website, distribute results on social media, and participate in outreach events aimed at high school students.

The project will systematically and quantitatively assess the role of CRs in regulating the state of the ISM and influencing galactic evolution in a variety of environments. The simulations will take advantage of a previously developed state-of-the art codebase (including magnetohydrodynamics, self-gravity, adaptive ray tracing, photochemistry, star cluster population synthesis for supernova and radiation feedback) and employ a new algorithm in which the propagation of CRs intimately depends on the properties of the multiphase ISM and CRs themselves.

This project will self-consistently treat star formation and the resulting UV heating and injection of mass, SN energy, and CRs because of stellar feedback, and will consider several environments as would be found in a Milky Way-like galaxy. The team will perform a suite of 3D shearing-box simulations of kpc-sized portions of galactic disks representative of galactic environments typical of Milky Way-like galaxies, with varying star formation rate, gas surface density, and gravitational potential.

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.