Abstract

We attempt to resolve the long-standing energy balance problem encountered by Radiative Transfer (RT) models, particularly in edge-on galaxies by incorporating a treatment for the clumpy structure of the Interstellar Medium (ISM). A subgrid approach is adopted, treating the quiescent dust clouds as pseudo-dust grains, with equivalent optical and thermal emission properties. Deriving key quantities such as the absorption, scattering and extinction cross-sections enables the virtualisation of the macroscopic clump into a microscopic pseudo-grain that can be included alongside the existing dust model constituents. The addition of the pseudo-grain results in a flatter extinction curve. A library of clump emission spectral energy distributions (SEDs) is constructed for radiation fields of various colours and intensities. The new clumpy model is applied to the edge-on galaxy NGC 891 and, for the first time, is able to achieve a good energy balance, simultaneously fitting both the submm and Near Infrared (NIR) data. The clumpy model is further applied to a small sample of seven galaxies of various inclinations, and the results are compared with those from the purely diffuse models. The clumpy models are characterised by a reduction in dust opacity, and therefore attenuation, compared to their purely diffuse counterparts. Thus, the maximum face-on optical depth in the B-band,