  Interstellar dust in galaxies can be traced either through its extinction
effects on the star light, or through its thermal emission at infrared
wavelengths. Recent radiative transfer studies of several nearby edge-on
galaxies have found an apparent inconsistency in the dust energy balance: the
radiative transfer models that successfully explain the optical extinction
underestimate the observed fluxes by an average factor of three. We investigate
the dust energy balance for IC4225 and NGC5166, two edge-on spiral galaxies
observed by the Herschel Space Observatory in the frame of the H-ATLAS survey.
We start from models which were constrained from optical data and extend them
to construct the entire spectral energy distribution of our galaxies. These
predicted values are subsequently compared to the observed far-infrared fluxes.
We find that including a young stellar population in the modelling is necessary
as it plays a non-negligible part in the heating of the dust grains. While the
modelling approach for both galaxies is nearly identical, we find two very
different results. As is often seen in other edge-on spiral galaxies, the
far-infrared emission of our radiative transfer model of IC4225 underestimates
the observed fluxes by a factor of about three. For NGC5166 on the other hand,
we find that both the predicted spectral energy distribution as well as the
simulated images match the observations particularly well. We explore possible
reasons for this difference and conclude that it is unlikely that one single
mechanism is the cause of the dust energy balance problem in spiral galaxies.
We discuss the different approaches that can be considered in order to get a
conclusive answer on the origin this discrepancy.
