High-resolution, 3D radiative transfer modelling III. The DustPedia
  barred galaxies
  Context: Dust in late-type galaxies in the local Universe is responsible for
absorbing approximately one third of the energy emitted by stars. It is often
assumed that dust heating is mainly attributable to the absorption of UV and
optical photons emitted by the youngest (<= 100 Myr) stars. Consequently,
thermal re-emission by dust at FIR wavelengths is often linked to the
star-formation activity of a galaxy. However, several studies argue that the
contribution to dust heating by much older stars might be more significant.
Advances in radiation transfer (RT) simulations finally allow us to actually
quantify the heating mechanisms of diffuse dust by the stellar radiation field.
  Aims: As one of the main goals in the DustPedia project, we have constructed
detailed 3D stellar and dust RT models for nearby galaxies. We analyse the
contribution of the different stellar populations to the dust heating in four
face-on barred galaxies: NGC1365, M83, M95, and M100. We aim to quantify the
fraction directly related to young stars, both globally and on local scales,
and to assess the influence of the bar on the heating fraction.
  Results: We derive global attenuation laws for each galaxy and confirm that
galaxies of high sSFR have shallower attenuation curves and weaker UV bumps. On
average, 36.5% of the bolometric luminosity is absorbed by dust. We report a
clear effect of the bar structure on the radial profiles of the dust-heating
fraction by the young stars, and the dust temperature. We find that the young
stars are the main contributors to the dust heating, donating, on average ~59%
of their luminosity to this purpose throughout the galaxy. This dust-heating
fraction drops to ~53% in the bar region and ~38% in the bulge region where the
old stars are the dominant contributors to the dust heating. We also find a
strong link between the heating fraction by the young stars and the sSFR.
