Today's colloquium: Measuring the outflow of cosmic-ray electrons in star-forming and radio galaxies

© astron

In this talk, I present 1D cosmic ray transport models, numerically solving equations of pure advection and diffusion for the electrons and calculating synchrotron emission spectra. As a study in case, we apply these model to a small survey of 12 late-type edge-on galaxies and to low-frequency LOFAR observations of the nearby FRI radio galaxy 3C31. We measure advection speeds, diffusion coefficients and magnetic field scale heights and lengths, which allow us to study magnetic field strengths without the assumption of "local" energy equipartition.

We find that our galaxies are either diffusion dominated (no outflow) or advection dominated (outflow), where the cosmic-ray electrons can partially leave the galaxy (non-calorimetric halo) and the advection speed is similar to the escape velocity, indicative of a galactic wind. In the FRI galaxy we extend the known source size by 15 per cent to 1 Mpc, so that advection speeds of 2000-3000 km/s result in a dynamical age of 250 Myr.

Our models show the existence of non-calorimetric haloes in star-forming galaxies that can explain global energy equipartition, as suggested by models of the radio-SFR(FIR) relations. For radio galaxies, these models result in improved estimates of the source age and energy, important to quantify the AGN feedback in the Universe.