Cosmic rays in star-forming galaxies: transport, feedback, and non-thermal messengers

Supernovae ultimately deposit ~10% of their total energy in a population of relativistic cosmic rays that subsequently interact with the interstellar medium (ISM) via magnetic forces. Because these particles lose energy to radiation only slowly compared to the ~90% of the supernova energy that is deposited in the ISM as heat, they are a potentially important feedback mechanism in galaxies despite their comparatively small energy budget. Their effectiveness, however, depends crucially on the poorly-understood plasma processes that couple them to the bulk, neutral ISM. In this talk I introduce a new, physically-motivated model for the coupling between cosmic rays and the neutral, star-forming ISM, and show that it successfully predicts the gamma-ray spectra of resolved nearby galaxies, the galactic IR-gamma correlation, and the cosmological gamma-ray background. I conclude by exploring the implications of this model for the importance of cosmic ray feedback, demonstrating that this mechanism is likely unimportant for rapidly star-forming galaxies either today or in the early universe, but may be critical for local dwarfs and quiescent spirals.

Mark Krumholz (ANU)
Place: Meeting ID: 824 9700 7833 Passcode: 060437
Kohei Inayoshi
Thursday, March 10, 2022 - 3:30PM to Thursday, March 10, 2022 - 4:30PM
I am a theoretical and computational astrophysicist at the Research School of Astronomy & Astrophysics at Australian National University. My research focuses on the formation of stars and galaxies, and on the physics of the interstellar medium. I approach these problems using a mix of analytic and numerical techniques.