Document Type


Publication Date



Physiology and Biophysics


The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), asymmetry (A), smoothness (S), the Gini index (G), the relative contribution of the brightest pixels to the secondorder moment of the flux (M20), ellipticity (E), and the Gini index of the second-order moment (GM) have all been applied to morphologically classify galaxies at various wavelengths. Here, we present a catalog of these parameters for the Spitzer Survey of stellar structure in Galaxies, a volume-limited, near-infrared (NIR) imaging survey of nearby galaxies using the 3.6 and 4.5μm channels of the Infrared Array Camera on board the Spitzer Space Telescope. Our goal is to provide a reference catalog of NIR quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, noninteracting galaxies—those typically found on the Hubble tuning fork—lie in this parameter space and show that there is a tight relation between concentration (C82) and M20 for normal galaxies. M20 can be used to classify galaxies into earlier and later types (i.e., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer NIR imaging. We find that four relations, based on the parameters A and S, G and M20, GM, C, and M20, respectively, select outliers in morphological parameter space, but each selects different subsets of galaxies. Two criteria (GM > 0.6, G > −0.115 × M20 + 0.384) seem most appropriate to identify possible mergers and the merger fraction in NIR surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on concentration and M20.


Copyright 2014. The American Astronomical Society. All rights reserved.

Original Publication Information

Holwerda, B. W., et al. "Morphological Parameters of a Spitzer Survey of Stellar Structure in Galaxies." 2014. The Astrophysical Journal 781(1): 19 pp.