Constraints on cosmic ray propagation from radio continuum data of NGC 2146

We present high-sensitivity multi-frequency radio continuum observations ofthe starburst galaxy NGC~2146. We have fitted these data with athree-dimensional diffusion model. The model can describe the radio emissionfrom the inner disk of NGC~2146 well, indicating that diffusion is the dominantmode of propagation in this region. Our results are indicating that NGC~2146has recently undergone a starburst, the star forming activity being located ina central bar. The spatial variation of the radio emission and of the spectralindex yield tight constraints on the diffusion coefficient $D_0$ and the energydependence of the diffusion. Away from the central bar of the galaxy the radioemission becomes filamentary and the diffusion model was found to be a poor fitto the data in these regions; we attribute this to different transportprocesses being important in the halo of the galaxy.Comment: 9 pages, 19 postscript figure, MNRAS-Latex (including the style-file), Accepted for publication in the Monthly Not. Roy. Astro.. So