Morphological Parameters of Spitzer Survey of Stellar Structure in
  Galaxies (S4G)
  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), relative contribution of the brightest pixels to the second
order 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 (S4G), a volume-limited
near-infrared imaging survey of nearby galaxies using the 3.6 and 4.5 micron
channels of the IRAC camera. Our goal is to provide a reference catalog of
near-infrared quantified morphology for high-redshift studies and galaxy
evolution models with enough detail to resolve stellar mass morphology.
  We explore where normal, non-interacting galaxies -those typically found on
the Hubble tuning fork- lie in this parameter space and show that there is a
tight relation between Concentration and M20 for normal galaxies. M20 can be
used to classify galaxies into earlier and later types (e.g., 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 near-infrared imaging. We find that four relations, based on the
parameters A&S, G&M20, GM, and C&M20, respectively, select outliers in the
morphological parameter space, but each selects different subsets of galaxies.
Two criteria (GM > 0.6, G > -0.115 x M20 + 0.384) seem most appropriate to
identify possible mergers and the merger fraction in near-infrared 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.
