Spiral structure in nearby galaxies II. comparative analysis and conclusions

TL;DR

This study analyzes two-armed spiral structures in nearby galaxies, revealing weak correlations with galaxy morphology but strong links to tidal interactions, and examining the relationship between stellar and gas spiral features.

Contribution

It provides a comparative analysis of spiral arm properties using infrared and visible imaging, highlighting the role of tidal forces and bars in spiral structure formation.

Findings

Weak correlation between spiral morphology and galaxy parameters.

Strong link between spiral arm strength and tidal interactions.

Loosely correlated pitch angles of stellar and gas arms.

Abstract

This paper presents a detailed analysis of two-armed spiral structure in a sample of galax- ies from the Spitzer Infrared Nearby Galaxies Survey (SINGS), with particular focus on the relationships between the properties of the spiral pattern in the stellar disc and the global struc- ture and environment of the parent galaxies. Following Paper I we have used a combination of Spitzer Space Telescope mid-infrared imaging and visible multi-colour imaging to isolate the spiral pattern in the underlying stellar discs, and we examine the systematic behaviours of the observed amplitudes and shapes (pitch angles) of these spirals. In general, spiral morphology is found to correlate only weakly at best with morphological parameters such as stellar mass, gas fraction, disc/bulge ratio, and vflat. In contrast to weak correlations with galaxy structure a strong link is found between the strength of the spiral arms and tidal forcing from nearby companion galaxies. This appears to support the longstanding suggestion that either a tidal interaction or strong bar is a necessary condition for driving grand-design spiral structure. The pitch angles of the stellar arms are only loosely correlated with the pitch angles of the corresponding arms traced in gas and young stars. We find that the strength of the shock in the gas and the contrast in the star formation rate are strongly correlated with the stellar spiral amplitude.