HERschel Observations of Edge-on Spirals (HEROES). IV. Dust energy
  balance problem
  We present results of the detailed dust energy balance study for the seven
large edge-on galaxies in the HEROES sample using 3D radiative transfer (RT)
modelling. Based on available optical and near-infrared observations of the
HEROES galaxies, we derive the 3D distribution of stars and dust in these
galaxies. For the sake of uniformity, we apply the same technique to retrieve
galaxy properties for the entire sample: we use a stellar model consisting of a
S\'ersic bulge and three double-exponential discs (a superthin disc for a young
stellar population and thin and thick discs for old populations). For the dust
component, we adopt a double-exponential disc with the new THEMIS dust-grain
model. We fit oligochromatic radiative transfer (RT) models to the optical and
near-infrared images with the fitting algorithm FitSKIRT and do panchromatic
simulations with the SKIRT code at wavelengths ranging from ultraviolet to
submillimeter. We confirm the previously stated dust energy balance problem in
galaxies: for the HEROES galaxies, the dust emission derived from our RT
calculations underestimates the real observations by a factor 1.5-4 for all
galaxies except NGC 973 and NGC 5907 (apparently, the latter galaxy has a more
complex geometry than we used). The comparison between our RT simulations and
the observations at mid-infrared-submillimeter wavelengths shows that most of
our galaxies exhibit complex dust morphologies (possible spiral arms,
star-forming regions, more extended dust structure in the radial and vertical
directions). We suggest that, in agreement with the results from Saftly et al.
(2015), the large- and small-scale structure is the most probable explanation
for the dust energy balance problem.
