  We study the effects of dust in hydrodynamic simulations of spiral galaxies
when different radial metallicity gradients are assumed. SUNRISE, a Monte-Carlo
radiative-transfer code, is used to make detailed calculations of the internal
extinction of disk galaxies caused by their dust content.
  SUNRISE is used on eight different Smooth Particle Hydrodynamics (SPH)
simulations of isolated spiral galaxies. These galaxies vary mainly in mass and
hence luminosity, spanning a range in luminosities from -16 to -22 magnitudes
in the B band. We focus on the attenuation in different wavelength bands as a
function of the disk inclination and the luminosity of the models, and compare
this to observations.
  Observations suggest different metallicity gradients for galaxies of
different luminosities. These metallicity gradients were explored in our
different models, finding that the resulting dust attenuation matches
observations for edge-on galaxies, but do not show a linear behaviour in log
axis ratio as some observations have suggested. A quadratic law describing the
dependence of attenuation on inclination, as proposed by more recent
observations, reconciles the attenuation of the simulations at intermediate
inclinations with observations. We also compare the total
infrared-to-ultraviolet flux ratios for the simulated galaxies with those of
the SINGS sample and find general agreement. Finally we compare our results
with those from simpler models that do not take into account structure such as
spiral arms, finding that the inclusion of sub-structure on the size scale of
spiral arms does not change conclusions about the attenuation dependence on
inclination or wavelength.
