Cosmic Ray Electron transport in the external galaxy M51

Paper in proceeding, 2024

Recent measurements of the synchrotron emission of the external galaxy M51 give indirect implications for the cosmic-ray electron (CRE) transport in the interstellar medium. In its face-on geometry, a radial resolved measurement of the star formation rate and the magnetic field strength is possible. Additionally, the diffusion coefficient can be inferred and seems to be energy independent. By modelling the CRE transport considering all relevant energy loss processes, we aim to distinguish the contribution of diffusive and advective transport. Therefore, we use the publicly available transport code CRPropa3.2 to solve the 3D transport equation. With our best-fit model, the data can be described well. For the best fit, the wind speed followed from the observation of the star formation rate must be decreased by a factor 5. We find that the inner galaxy is dominated by advection and the outer is composed by both spatial diffusion and advection. In general, this approach of modelling face-on galaxies gives insights to the only indirect observable advection profile.