Grand Design and Flocculent Spirals in the Spitzer Survey of Stellar Structure in Galaxies (S4G)

TL;DR

This study analyzes spiral arm structures in 46 galaxies from the S4G survey at 3.6 microns, revealing differences in arm properties across galaxy types and the influence of bars on spiral structure.

Contribution

It provides the first comprehensive mid-infrared analysis of spiral arm properties across various galaxy types, highlighting the relationship between stellar structures, star formation, and bars.

Findings

Most flocculent galaxies are also flocculent in the mid-IR.

Arm-interarm contrast increases from flocculent to grand design galaxies.

Bars are longer and more prominent in early-type spirals.

Abstract

Spiral arm properties of 46 galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G) were measured at 3.6mu, where extinction is small and the old stars dominate. The sample includes flocculent, multiple arm, and grand design types with a wide range of Hubble and bar types. We find that most optically flocculent galaxies are also flocculent in the mid-IR because of star formation uncorrelated with stellar density waves, whereas multiple arm and grand design galaxies have underlying stellar waves. Arm-interarm contrasts increase from flocculent to multiple arm to grand design galaxies and with later Hubble types. Structure can be traced further out in the disk than in previous surveys. Some spirals peak at mid-radius while others continuously rise or fall, depending on Hubble and bar type. We find evidence for regular and symmetric modulations of the arm strength in NGC 4321. Bars tend to be long, high amplitude, and flat-profiled in early type spirals, with arm contrasts that decrease with radius beyond the end of the bar, and they tend to be short, low amplitude, and exponential-profiled in late Hubble types, with arm contrasts that are constant or increase with radius. Longer bars tend to have larger amplitudes and stronger arms.