The sequence of spiral arm classes: Observational signatures of persistent spiral density waves in grand-design galaxies

TL;DR

This study analyzes the properties of spiral arms in galaxies, revealing that grand-design galaxies with classical bulges support persistent spiral density waves, and highlighting correlations between bulge, bar, and arm features.

Contribution

It provides observational evidence linking classical bulges to stable spiral density waves in grand-design galaxies, using new measurements of arm-interarm luminosity contrasts.

Findings

Flocculent galaxies have lower stellar mass and surface density.

Grand-design and multi-armed galaxies share similar fundamental parameters.

Classical bulges are associated with standing spiral wave modes.

Abstract

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.