  Spatial correlations between spiral arms and other galactic components such
as giant molecular clouds and massive OB stars suggest that spiral arms can
play vital roles in various aspects of disk galaxy evolution. Segmentation of
spiral arms in disk galaxies is therefore a key task to investigate these
correlations. We here try to decompose disk galaxies into spiral and non-spiral
regions by using U-net, which is based on deep learning algorithms and has been
invented for segmentation tasks in biology.
