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 micron surface brightness ratios tend to be more
strongly influenced by star forming regions. However, the 250/350 micron and
350/500 micron surface brightness ratios are more strongly affected by the
light from the total stellar populations, suggesting that the dust emission at
>250 microns originates predominantly from a component that is colder than the
dust seen at <160 microns 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.
