Catalogue of the morphological features in the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G)

TL;DR

This paper presents a comprehensive catalogue of morphological features in 2352 nearby galaxies from the S$^4$G survey, using 3.6 μm images to measure structures like bars, rings, and spiral arms, revealing correlations with galaxy mass.

Contribution

It provides the first detailed, human-supervised measurements of various galaxy structures at 3.6 μm, including novel insights into barlenses and their relation to bars and galaxy mass.

Findings

Normalized sizes of rings and lenses increase in less massive galaxies.

Bars in low-mass galaxies are less concentrated.

Evidence suggests barlenses are integral parts of bars and can evolve into lenses.

Abstract

A catalogue of the morphological features for the complete Spitzer Survey of Stellar Structure in Galaxies (S$^4$G), including 2352 nearby galaxies, is presented. The measurements are made using 3.6 $\mu$m images, largely tracing the old stellar population; at this wavelength the effects of dust are also minimal. The measured features are the sizes, ellipticities, and orientations of bars, rings, ringlenses, and lenses. Measured in a similar manner are also barlenses (lens-like structures embedded in the bars), which are not lenses in the usual sense, being rather the more face-on counterparts of the boxy/peanut structures in the edge-on view. In addition, pitch angles of spiral arm segments are measured for those galaxies where they can be reliably traced. More than one pitch angle may appear for a single galaxy. All measurements are made in a human-supervised manner so that attention is paid to each galaxy. We used isophotal analysis, unsharp masking, and fitting ellipses to measured structures. We find that the sizes of the inner rings and lenses normalized to barlength correlate with the galaxy mass: the normalized sizes increase toward the less massive galaxies; it has been suggested that this is related to the larger dark matter content in the bar region in these systems. Bars in the low mass galaxies are also less concentrated, likely to be connected to the mass cut-off in the appearance of the nuclear rings and lenses. We also show observational evidence that barlenses indeed form part of the bar, and that a large fraction of the inner lenses in the non-barred galaxies could be former barlenses in which the thin outer bar component has dissolved.