A New Approach to Galaxy Morphology. I. Analysis of the Sloan Digital Sky Survey Early Data Release

By R. Abraham, S. van den Bergh, P. Nair. 2003

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In this paper we present a new statistic for quantifying galaxy morphology based on measurements of the Gini coefficient of galaxy light distributions. This statistic is easy to measure and is commonly used in econometrics to measure how wealth is distributed in human populations. When applied to galaxy images, the Gini coefficient provides a quantitative measure of the inequality with which a galaxy's light is distributed among its constituent pixels. We measure the Gini coefficient of local galaxies in the Early Data Release of the Sloan Digital Sky Survey and demonstrate that this quantity is closely correlated with measurements of central concentration, but with significant scatter. This scatter is almost entirely due to variations in the mean surface brightness of galaxies. By exploring the distribution of galaxies in the three-dimensional parameter space defined by the Gini coefficient, central concentration, and mean surface brightness, we show that all nearby galaxies lie on a well-defined two-dimensional surface (a slightly warped plane) embedded within a three-dimensional parameter space. By associating each galaxy sample with the equation of this plane, we can encode the morphological composition of the entire SDSS g*-band sample using the following three numbers: {22.451, 5.366, 7.010}. The i*-band sample is encoded as {22.149, 5.373, and 7.627}.

Subfields: Astronomy and Astrophysics, Ecology

View Paper: https://www.semanticscholar.org/paper/379bd41fd0a7bfb3dbf2d87bc47c708f322a0274

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Citations in the corpus

Galaxy merger morphologies and time-scales from simulations of equal-mass gas-rich disc mergers (2008, methodology): “The Gini coefficient G is a statistic based on the Lorenz curve, the rank-ordered cumulative distribution function of a population’s wealth or, in this case, a galaxy’s pixel values (Abraham et al. 2003).”
The Rest-Frame Far-Ultraviolet Morphologies of Star-Forming Galaxies at z ~ 1.5 and 4 (2006, methodology): “First presented in Lotz et al. (2004; hereafter LPM04), this technique measures the relative distribution of galaxy pixel flux values or Gini coefficient (G ) (Abraham et al. 2003) and the second-order moment of the brightest 20% of the galaxy’s pixels (M20).”
Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars (2007, methodology): “This seems to be the case in the systems with the highest E(B V ) in our sample, while the hosts of quasars with lower E(B V ) tend to have both Gini coefficients and concentration indices more consistent with those of normal, undisturbed galaxies Abraham et al. (2003).”
Revisiting the Hubble sequence in the SDSS DR7 spectroscopic sample: a publicly available Bayesian automated classification (2010, methodology): “…simple way by measuring some parameters, such as concentration, asymmetry, clumpiness, Gini index (e.g. Abraham et al. 1996; Conselice et al. 2000; Abraham et al. 2003) or through 1D (Prieto et al. 2001; Trujillo et al. 2001) or 2D-fitting algorithms (e.g. Simard et al. 2002; Peng et al. 2002; de…”
Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies (2009, methodology): “Another pair of parameters used in this fashion are the Gini-coefficient (G) (Abraham et al. 2003) and secondorder moment of the brightest 20% of the galaxy’s light (M20), most notably by Lotz et al. (2008a).”
Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey (2017, background): “…of the light concentration, asymmetry and smooth- ness/clumpiness (hereafter, CAS measurements; see Bershady et al. 2000; Conselice 2003), as well as other measures involving the Gini index and the second-order moments of the light distributions (see Abraham et al. 2003; Lotz et al. 2004, 2008).”
Morphology Segregation of Galaxies in Color-Color Gradient Space (2005, background): “Endeavors to develop an objective, automatic, and successful morphology classifier applicable to large libraries of digital images have resulted in various schemes (Yamauchi et al. 2005; Blanton et al. 2003b; Abraham et al. 1996, 2003; Strateva et al. 2001; Shimasaku et al. 2001; Doi et al. 1993).”
Deep GALEX Imaging of the COSMOS HST Field: A First Look at the Morphology of z ~ 0.7 Star-forming Galaxies (2007, methodology): “We therefore chose to follow the work of Abraham et al. (1996b), Conselice et al. (2000), Conselice (2003), Abraham et al. (2003) and Lotz et al. (2004) and use their non-parametric approaches, thus computing Concentration(C), Asymmetry(A) and Clumpiness(S) parameters (Conselice 2003), as well as…”
zCOSMOS – 10k-bright spectroscopic sample - The bimodality in the galaxy stellar mass function: exploring its evolution with redshift (2009, methodology): “…structure by performing a principal component analysis (PCA) in the five-dimensional parameter space of asymmetry (A), concentration (C), Gini coefficient (G), the secondorder moment of the brightest 20% galaxy pixels (M20; Abraham et al. 2003), and the ellipticity of the light distribution (ǫ).”
The structures of distant galaxies – I. Galaxy structures and the merger rate to z∼ 3 in the Hubble Ultra-Deep Field (2007, background): “4.3.3 The Gini-M20 plane In addition to the CAS values, the newer Gini and the M20 coefficients also give information on morphological characteristics of galaxies (e.g., Abraham et al. 2003; Lotz et al. 2004; Lotz et al. 2006).”
The Evolution of Galaxy Structure Over Cosmic Time (2014, methodology): “2.3.4 Other Coefficients Another popular structural measurement system is the Gini/M20 parameters which are used in a similar way to the CAS parameters to find galaxies of broad morphological types, especially galaxies undergoing mergers (e.g., Abraham et al. 2003; Lotz et al. 2004).”
The Physical Nature of Rest-UV Galaxy Morphology during the Peak Epoch of Galaxy Formation (2006, positive): “We therefore favor a non-parametric approach to classification similar to that discussed by Abraham et al. (2003), LPM04, and Lotz et al. (2006) who define the gini coefficient G as a measure of the uniformity of the flux distribution within a source.”