A Model for Cosmic Ray Interactions in M82

Tova Yoast-Hull (University of Wisconsin)

From first principles, we construct a simple model for the evolution of energetic particles in the starburst galaxy M82. Assuming constant cosmic-ray acceleration efficiency with Milky Way parameters, we calculate the cosmic-ray proton and primary & secondary electron/positron populations. From the cosmic-ray spectra, we can predict the radio synchrotron and gamma-ray spectrum. To more accurately model the radio spectrum, we incorporate a multiphase interstellar medium in the starburst region of M82. The spectra for this simple model are compared to the observed radio and gamma-ray spectra of M82. Chi-squared tests are used to compare with radio observations to find the best-fit parameters. The best-fit model yields constraints on the magnetic field strength and advection speed for the starburst zone in M82. Fermi detections of M82 provide additional constraints for the advection speed. Through this project, we aim to check the calorimeter model, in which energetic particles lose most of their energy within the galaxy. We also explore whether we can apply our knowledge of cosmic ray acceleration and propagation as we understand them in the Milky Way to starburst systems.