One of the largest unknowns in galaxy evolution is the role played by cosmic rays — the non-thermal particles that are accelerated by supernova shocks and then suffuse interstellar and circumgalactic gas. While observed energy density of cosmic rays around the Sun is high enough that they are potentially important, they interact with the thermal gas around them mostly via poorly understood magnetically-driven plasma processes, and thus it is uncertain how much force they are able to exert on the gas through which they move. The range of allowed plasma physics models is very large, ranging from those that imply that cosmic rays are the primary drivers of phenomena such as galactic winds, to those that imply cosmic rays are dynamically unimportant.

Fortunately, recent and upcoming gamma-ray observations provide an opportunity to resolve this dilemma. While different plasma physics models imply different dynamics, they also imply substantial differences in features of the gamma-ray sky, for example how the shape of the gamma-ray spectrum changes as a function of distance off the Galactic plane, or how much it varies from one line of sight to another. The goal of this project is to make predictions for the observable gamma-ray signatures of different plasma physics models for cosmic ray transport by combining state-of-the art simulations of the Galactic disc (such as the one shown in the figure) and cosmic ray transport. The predicted observational signatures can then be checked against existing data from the Fermi satellite and upcoming data from the Cherenkov Telescope Array in order to constrain the plasma models.

Relevant papers: 

https://ui.adsabs.harvard.edu/abs/2022MNRAS.517.1355K/abstract

https://ui.adsabs.harvard.edu/abs/2023MNRAS.523.2608R/abstract