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 t
he 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.
We study the Kennicutt-Schmidt star formation law and efficiency in the gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on its unusually large atomic gas (HI) disk (r_HI/r_25 = 3.5, r_25 = 1.85). We present deep GALEX near
and far ultraviolet observations, used as a recent star formation tracer, and we compare them with new, high resolution (16, or 1.6 kpc) VLA HI observations. The UV and HI maps show good spatial correlation outside the inner 1, where the HI phase dominates over H_2. Star-forming regions in the extended gaseous disk are mainly located along the enhanced HI emission within two (relatively) symmetric giant gaseous spiral arm-like features, which emulate a HI pseudo-ring at a r simeq 3 . Inside such structure, two smaller gaseous spiral arms extend from the NE and SW of the optical disk and connect to the previously mentioned HI pseudo-ring. Interestingly, we find that the (atomic) Kennicutt-Schmidt power law index systematically decreases with radius, from N simeq 3.0 +- 0.3 in the inner disk (0.8 - 1.7) to N = 1.6 +- 0.5 in the outskirts of the gaseous disk (3.3 - 4.2). Although the star formation efficiency (SFE), the star formation rate per unit of gas, decreases with radius where the HI component dominates as is common in galaxies, we find that there is a break of the correlation at r = 1.5 r_25. At radii 1.5 r_25 < r < 3.5 r_25, mostly within the HI pseudo-ring structure, there exist regions whose SFE remains nearly constant, SFE simeq 10^-11 yr^-1. We discuss about possible mechanisms that might be triggering the star formation in the outskirts of this galaxy, and we suggest that the constant SFE for such large radii r > 2 r_25 and at such low surface densities might be a common characteristic in extended UV disk galaxies.
