Investigations of dust heating in M81, M83 and NGC 2403 with the Herschel Space Observatory

We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground-based optical and near-infrared data to understand how dust heating in the nearby face-on spiral galaxies M81, M83 and NGC 2403 is affected by the starlight from all stars and by the radiation from star-forming regions. We find that 70/160 μm surface brightness ratios tend to be more strongly influenced by star-forming regions. However, the 250/350 μm and 350/500 μm surface brightness ratios are more strongly affected by the light from the total stellar populations, suggesting that the dust emission at >250 μm originates predominantly from a component that is colder than the dust seen at <160 μm and that is relatively unaffected by star formation activity. We conclude by discussing the implications of this for modelling the spectral energy distributions of both nearby and more distant galaxies and for using far-infrared dust emission to trace star formation.