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 ( M _ { 20 } ) , ellipticity ( E ) , and the Gini index of the second order moment ( G _ { M } ) 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 ( S ^ { 4 } G ) , a volume-limited near-infrared imaging survey of nearby galaxies using the 3.6 and 4.5 \mu m channels of the IRAC camera onboard Spitzer Space Telescope .
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 ( C _ { 82 } ) and M _ { 20 } Â for normal galaxies . M _ { 20 } Â 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 and S , G and M _ { 20 } , G _ { M } , and C and M _ { 20 } , respectively , select outliers in the morphological parameter space , but each selects different subsets of galaxies .
Two criteria ( G _ { M } > 0.6 , G > -0.115 \times M _ { 20 } +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 M _ { 20 } .