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J/ApJ/781/12 Morphological parameters of galaxies from Spitzer (Holwerda+, 2014)

Morphological parameters of a Spitzer survey of stellar structure in galaxies. Holwerda B.W., Munoz-Mateos J.-C., Comeron S., Meidt S., Sheth K., Laine S., Hinz J.L., Regan M.W., Gil de Paz A., Menendez-Delmestre K., Seibert M., Kim T., Mizusawa T., Laurikainen E., Salo H., Laine J., Gadotti D.A., Zaritsky D., Erroz-Ferrer S., Ho L.C., Knapen J.H., Athanassoula E., Bosma A., Pirzkal N. <Astrophys. J., 781, 12 (2014)> =2014ApJ...781...12H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxy catalogs ; Morphology Keywords: galaxies: elliptical and lenticular, cD - galaxies: general - galaxies: irregular - galaxies: spiral - galaxies: statistics - galaxies: stellar content - galaxies: structure Abstract: 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 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, 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, 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 (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>-0.115xM20+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. Description: The Spitzer Survey of stellar structure in Galaxies (S4G; Sheth et al. 2010, cat. J/PASP/122/1397; http://www.cv.nrao.edu/~ksheth/s4g) is a volume-, magnitude-, and size-limited (D<40Mpc,|b|>30°,mBcorr<15.5,D25>1') survey of 2349 nearby galaxies in 3.6µm and 4.5µm (IRAC channels 1 and 2) of the IRAC of the Spitzer Space Telescope, using both archival cryogenic and ongoing warm-mission observations (for a full description and selection criteria, see Sheth et al. 2010, cat. J/PASP/122/1397). All images have been reprocessed by the S4G pipeline. The reprocessed pixel scale is 0.75''; the resolution is 1.7'' for 3.6µm and 1.6'' for 4.5µm. The data have been made public (http://irsa.ipac.caltech.edu/data/SPITZER/S4G/). For this paper, we use the first and second pipeline products (P1 and P2) of S4G (M. W. Regan et al., in preparation) available from DR1 (2013 January) for 2349 galaxies: the photometry images (phot) from P1 and foreground and background object masks from P2 for both the 3.6 and 4.5µm images (see for more details Sheth et al. 2010, cat. J/PASP/122/1397). Our morphological parameters are in concert with the final S4G data products (J.-C. Munoz-Mateos et al., in preparation). The Tables A1 and A2 present the full catalog of morphological parameters for the S4G sample of galaxies for the 3.6 and 4.5µm. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file tablea1.dat 81 2345 The morphological parameters at 3.6µm for the 2349 S4G galaxies tablea2.dat 81 2345 The morphological parameters at 4.5µm for the 2349 S4G galaxies
See also: VII/237 : HYPERLEDA. I. Catalog of galaxies (Paturel+, 2003) J/MNRAS/416/2415 : Morphological parameters of WHISP galaxies (Holwerda+, 2011) J/PASP/122/1397 : Spitzer Survey of Galaxies Stellar Structure (Sheth+, 2010) J/AJ/128/163 : Galaxy morphological classification (Lotz+, 2004) J/ApJS/147/1 : Classification of nearby galaxies (Conselice+, 2003) J/ApJ/588/218 : i*g* photometry of SDSS EDR galaxies (Abraham+, 2003) http://www.cv.nrao.edu/~ksheth/s4g : S4G survey Byte-by-byte Description of file: tablea[12].dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Galaxy identifier (1) 12- 15 F4.2 --- Gini [0/1] The Gini index (indicator of equality: 1=all the flux is in one pixel, 0=all the pixels in the object have equal values) (2) 17- 20 F4.2 --- e_Gini [0/10]? The uncertainty in Gini 22- 26 F5.2 --- M20 [-4.7/-0.06] Relative contribution of brightest pixels to 2nd order moment of flux (M20) (3) 28- 31 F4.2 --- e_M20 [0/10] The uncertainty in M20 33- 36 F4.2 --- C82 [0/9.2] The concentration index (C82) (4) 38- 41 F4.2 --- e_C82 [0/1.9] The uncertainty in C82 43- 46 F4.2 --- A [0.07/1] The asymmetry parameter (5) 48- 51 F4.2 --- e_A [0/5]? The uncertainty in A 53- 56 F4.2 --- S [0.04/1.7] The smoothness parameter (6) 58- 61 F4.2 --- e_S [0/7]? The uncertainty in S 63- 66 F4.2 --- Ell [0/1] The ellipticity parameter (7) 68- 71 F4.2 --- e_Ell [0/0.25]? The uncertainty in Ell 73- 76 F4.2 --- GM [0.2/1] The Gini index of 2nd order moment (GM) (8) 78- 81 F4.2 --- e_GM [0/10]? The uncertainty in GM
Note (1): There are only 2345 objects in the tables because the code crashed when calculating the parameters for 4 objects. We use the concentration-asymmetry-smoothness (CAS) system from Bershady et al. (2000AJ....119.2645B), Conselice et al. (2000ApJ...529..886C), and Conselice 2003 (cat. J/ApJS/147/1), the Gini and M20 system from Lotz et al. 2004 (cat. J/AJ/128/163), and a hybrid parameter GM, the Gini parameter of the second-order moment (Holwerda et al., 2011MNRAS.416.2426H). Note (2): The Gini parameter is an economic indicator of equality (G=1 if all the flux is in one pixel and G=0 if all the pixels in the object have equal values). We use the implementation from Abraham et al. 2003 (cat. J/ApJ/588/218) and Lotz et al. 2004 (cat. J/AJ/128/163): G = [1/<I>n(n-1)]∑i(2i-n-1)|Ii| (Eq.(4) in the paper), where Ii is the intensity of pixel i in an increasing flux-ordered list of the n pixels in the object and <I> is the mean pixel intensity. B. W. Holwerda et al. (in preparation) find a weak link between Gini and current star formation. Note (3): The relative second-order moment of the brightest 20% of the flux: M20 = log(∑kiMi/Mtot), for which ∑kiIi<0.2Itot is true (Eq.(6) in the paper), where pixel K marks the top 20% point in the flux-ordered pixel list. The M20 parameter is a parameter that is sensitive to bright structure away from the center of the galaxy; the flux is weighted in favor of the outer parts. It therefore is relatively sensitive to tidal structures (provided of course that these are included in the calculation), specifically star-forming regions formed in the outer spiral or tidal arms. If no such structures are in the image, the 20% brightest pixels will most likely be concentrated in the center of the galaxy, which is weighted lower. Thus, one can expect low values of M20 for smooth galaxies with bright nuclei (ellipticals, S0, or Sa) but much higher values (less negative) for galaxies with extended arms featuring bright HII regions. Note (4): The log of the ratio of the radii including 80 over 20% of the flux. Concentration is defined as Kent (1985ApJS...59..115K): C82 = 5log(r80/r20) (Eq.(1) in the paper), where r% is the radius of the circular aperture that includes that percentage of the total light of the object. Note (5): In an image with n pixels with intensities I(i,j) at pixel positions (i,j), in which the value of the pixel is I180(i,j) in the image rotated by 180°, asymmetry is defined as (Schade et al., 1995ApJ...451L...1S; Conselice 2003, cat. J/ApJS/147/1): A = ∑i,j|I(i,j)-I180(i,j)|/2∑i,j|I(i,j)| (Eq.(2) in the paper). Note (6): Smoothness (also called clumpiness in the original Conselice 2003, cat. J/ApJS/147/1) is defined as: S = ∑i,j|I(i,j)-IS(i,j)|/∑i,j|I(i,j)| (Eq.(3) in the paper), where IS(i,j) is the same pixel in the image after smoothing with a choice of kernel. Note (7): Scarlata et al. (2007ApJS..172..406S) added the ellipticity of a galaxy's image to the mix of parameters in order to classify galaxies according to type in the COSMOS field. Ellipticity is defined as: E = 1-b/a (Eq.(8) in the paper), where a and b are the major and minor axes of the galaxy, respectively, computed from the spatial second-order moments of the light along the x- and y-axes of the image in the same manner as SExtractor. We include this definition for completeness. Note (8): Instead of the intensity of the pixel (Ii), one can use the second-order moment of the pixel (Mi=Ii[(xi-xc)2+(yi-yc)2]) in Eq.(4). This is the GM parameter (Holwerda et al., 2011MNRAS.416.2426H): GM = [1/<M>n(n-1)]∑i(2i-n-1)|Mi| (Eq.(7) in the paper), which is an indication of the spread of pixel values weighted with the projected radial distance to the galaxy center. In essence, this is the Gini parameter with a different weighting scheme than unity for each pixel. Similar to the M20 parameter, it emphasizes the flux from the outer regions of the galaxy. If there is significant flux in the outer parts, this will boost the value of GM. Contrary to M20, it does not depend on a somewhat arbitrary delineation of the brightest 20% flux for the denominator but relies on all pixel values. Unlike the Gini parameter, however, it does rely on a supplied center of the galaxy (to compute Mi). For concentrated galaxies, the GM and Gini values will be close together, but as relatively more flux is evident in the outer parts of the galaxy, GM will be higher. Holwerda et al. 2011 (cat. J/MNRAS/416/2415) found GM to be a good single parameter to identify active mergers (sweeping tidal tails, etc.) from atomic hydrogen maps (HI).
History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 12-Nov-2015
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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