Radiation fields in star-forming galaxies: the disc, thin disc and bulge

We provide and describe a library of diffuse stellar radiation fields in spiral galaxies derived using calculations of the transfer of stellar radiation from the main morphological components - discs, thin discs and bulges - through the dusty interstellar medium. These radiation fields are self-consistent with the solutions for the integrated panchromatic spectral energy distributions (SEDs) previously presented using the same model. Because of this, observables calculated from the radiation fields, such as gamma-ray or radio emission, can be self-consistently combined with the solutions for the ultraviolet/optical/submillimetre SEDs, thus expanding the range of applicability of the radiation transfer model to a broader range of wavelengths and physical quantities. We also give analytic solutions for radiation fields in optically thin stellar discs, in stellar discs with one dust disc and in stellar discs with two dust discs. The analytic solutions for the direct light are exact and can be used as benchmarks. The analytic solutions with scattering are only approximate, becoming exact only in the extreme optically thick limit. We find strongly contrasting solutions for the spatial distribution of the radiation fields for discs, thin discs and bulges. For bulges, we find a strong dependence of the radiation fields on the Sérsic index.