Ultraviolet Radiative Transfer Modeling of Nearby Galaxies with
  Extraplanar Dusts
  In order to examine their relation to the host galaxy, the extraplanar dust
of six nearby galaxies are modeled, employing a three dimensional Monte Carlo
radiative transfer code. The targets are from the highly-inclined galaxies that
show dust-scattered ultraviolet halos, and the archival Galaxy Evolution
Explorer FUV band images were fitted with the model. The observed images are in
general well reproduced by two dust layers and one light-source layer, whose
vertical and radial distributions have exponential profiles. We obtained
several important physical parameters, such as star formation rate (SFR_UV),
face-on optical depth, and scale-heights. Three galaxies (NGC 891, NGC 3628,
and UGC 11794) show clear evidence for the existence of extraplanar dust layer.
However, it is found that the rest three targets (IC 5249, NGC 24, and NGC
4173) do not necessarily need a thick dust disk to model the ultraviolet (UV)
halo, because its contribution is too small and the UV halo may be caused by
the wing part of the GALEX point spread function. This indicates that the
galaxy samples reported to have UV halos may be contaminated by galaxies with
negligible extraplanar (halo) dust. The galaxies showing evidence of the
extraplanar dust layer fall within a narrow range on the scatter plots between
physical parameters such as SFR_UV and extraplanar dust mass. Several
mechanisms possible to produce the extraplanar dust are discussed. We also
found a hint that the extraplanar dust scale-height might not be much different
from the polycyclic aromatic hydrocarbon emission characteristic height.
