Harwit et al. The nonthermal radio luminosities of normal galaxies are correlated to different degrees with luminosities in most other wavebands, and these luminosity correlations have been used to support different stellar populations as sources of cosmic rays. Hummel et al. Since there is no end to correlations with radio luminosities, this is probably the most that can be said with confidence. Too few radio supernovae have been observed to establish radio supernova rates in galaxies.
Most cosmic rays escape their parent SNRs, filling the galaxy disk and halo.
Cosmic rays may also diffuse into a static halo or convect away from the disk into a dynamic halo.