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The morphology of galaxies can be quantified to some degree using a set ofscale-invariant parameters. Concentration (C), Asymmetry (A), Smoothness (S),the Gini index (G), relative contribution of the brightest pixels to the secondorder moment of the flux (M20), ellipticity (E), and the Gini index of thesecond order moment (GM) have all been applied to morphologically classifygalaxies at various wavelengths. Here we present a catalog of these parametersfor the Spitzer Survey of Stellar Structure in Galaxies (S4G), a volume-limitednear-infrared imaging survey of nearby galaxies using the 3.6 and 4.5 micronchannels of the IRAC camera. Our goal is to provide a reference catalog ofnear-infrared quantified morphology for high-redshift studies and galaxyevolution models with enough detail to resolve stellar mass morphology.  We explore where normal, non-interacting galaxies -those typically found onthe Hubble tuning fork- lie in this parameter space and show that there is atight relation between Concentration and M20 for normal galaxies. M20 can beused to classify galaxies into earlier and later types (e.g., to separatespirals from irregulars). Several criteria using these parameters exist toselect systems with a disturbed morphology, i.e., those that appear to beundergoing a tidal interaction. We examine the applicability of these criteriato Spitzer near-infrared imaging. We find that four relations, based on theparameters A&S, G&M20, GM, and C&M20, respectively, select outliers in themorphological parameter space, but each selects different subsets of galaxies.Two criteria (GM > 0.6, G > -0.115 x M20 + 0.384) seem most appropriate toidentify possible mergers and the merger fraction in near-infrared surveys. Wefind no strong relation between lopsidedness and most of these morphologicalparameters, except for a weak dependence of lopsidedness on Concentration andM20.

Morphological Parameters of Spitzer Survey of Stellar Structure in Galaxies (S4G)