The sequence of spiral arm classes: Observational signatures of
  persistent spiral density waves in grand-design galaxies
  We investigate how the properties of spiral arms relate to other fundamental
galaxy properties. To this end, we use previously published measurements of
those properties, and our own measurements of arm-interarm luminosity contrasts
for a large sample of galaxies, using 3.6$\mu$m images from the Spitzer Survey
of Stellar Structure in Galaxies. Flocculent galaxies are clearly distinguished
from other spiral arm classes, especially by their lower stellar mass and
surface density. Multi-armed and grand-design galaxies are similar in most of
their fundamental parameters, excluding some bar properties and the
bulge-to-total luminosity ratio. Based on these results, we discuss dense,
classical bulges as a necessary condition for standing spiral wave modes in
grand-design galaxies. We further find a strong correlation between
bulge-to-total ratio and bar contrast, and a weaker correlation between arm and
bar contrasts.
