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

The authors present high-sensitivity multi-frequency radio continuum observations of the starburst galaxy NGC 2146. The authors have fitted these data with a three-dimensional diffusion model. The model can describe the radio emission from the inner disc of NGC 2146 well, indicating that diffusion is the dominant mode of propagation in this region. The results indicate that NGC 2146 has recently undergone a starburst, the star-forming activity being located in a central bar. The spatial variations of the radio emission and of the spectral index yield tight constraints on the diffusion coefficient D₀ and the energy dependence of the diffusion. Away from the central bar of the galaxy the radio emission becomes filamentary and the diffusion model is found to be a poor fit to the data in these regions; the authors attribute this to different transport processes being important in the halo of the galaxy.