A New Nonparametric Approach to Galaxy Morphological Classification

By J. Lotz, Joel R. Primack, P. Madau. 2003

623 citations recorded by the source corpus.

We present two new nonparametric methods for quantifying galaxy morphology: the relative distribution of the galaxy pixel flux values (the Gini coefficient or G) and the second-order moment of the brightest 20% of the galaxy's flux (M20). We test the robustness of G and M20 to decreasing signal-to-noise ratio (S/N) and spatial resolution and find that both measures are reliable to within 10% for images with average S/N per pixel greater than 2 and resolutions better than 1000 and 500 pc, respectively. We have measured G and M20, as well as concentration (C), asymmetry (A), and clumpiness (S) in the rest-frame near-ultraviolet/optical wavelengths for 148 bright local "normal" Hubble-type galaxies (E–Sd) galaxies, 22 dwarf irregulars, and 73 0.05 < z < 0.25 ultraluminous infrared galaxies (ULIRGs). We find that most local galaxies follow a tight sequence in G-M20-C, where early types have high G and C and low M20 and late-type spirals have lower G and C and higher M20. The majority of ULIRGs lie above the normal galaxy G-M20 sequence because of their high G and M20 values. Their high Gini coefficients arise from very bright nuclei, while the high second-order moments are produced by multiple nuclei and bright tidal tails. All of these features are signatures of recent and on-going mergers and interactions. We also find that in combination with A and S, G is more effective than C at distinguishing ULIRGs from the "normal" Hubble types. Finally, we measure the morphologies of 491.7 < z < 3.8 galaxies from HST NICMOS observations of the Hubble Deep Field North. We find that many of the z ∼ 2 galaxies possess G and A higher than expected from degraded images of local elliptical and spiral galaxies and have morphologies more like low-redshift ULIRGs.

Subfields: Astronomy and Astrophysics, Computer Vision and Pattern Recognition, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/ef49ef03d3d8c3088c1b77e6e8b381c4d02b477d

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Citations in the corpus

Toward an Understanding of the Rapid Decline of the Cosmic Star Formation Rate (2005, background): “Awide range of morphological disturbance diagnostics must be developed and robustly tested (see, e.g., Conselice et al. 2003; Lotz et al. 2004 for some promising examples of this kind of technique).”
The ATLAS3D project - XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images (2014, methodology): “Automatic algorithm parametrizing galaxies with coefficients such as the CAS (Conselice 2003), Gini (Abraham et al. 2003), or M20 (Lotz et al. 2004), have been widely used for morphological classification of large number of galaxies, especially distant ones.”
HISTORY OF GALAXY INTERACTIONS AND THEIR IMPACT ON STAR FORMATION OVER THE LAST 7 Gyr FROM GEMS (2009, methodology): “…use automated parameters, such as CAS asymmetry A and clumpiness parameters (Conselice et al 2000; Conselice 2003) or Gini-M20 coefficients (e.g., Lotz et al. 2004) to identify merging galaxies can fail to pick stages of both major and minor mergers where distortions do not dominate the total…”
A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. I. Galaxy Mergers and Quasar Activity (2007, methodology): “…(and essentially all merging pairs) will be in this stage, and numerical simulations suggest it is the last stage at which the distinct nuclei enable automated morphological selection criteria to efficiently identify the system as a merger (Lotz et al. 2004; J. M. Lotz et al. 2008, in preparation).”
THE KILOPARSEC-SCALE KINEMATICS OF HIGH-REDSHIFT STAR-FORMING GALAXIES (2009, methodology): “…cut generally does not reach surface brightness levels as low as those of many narrowband studies; this results in lower values of G than are normally derived in the rest-frame UV (e.g., Lotz et al. 2004, 2006; Law et al. 2007b) as there is less contrast among pixels in the segmentation map.”
The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations (2018, methodology): “To facilitate the analysis of our synthetic and survey images, we have developed statmorph, a Python package for calculating non-parametric morphologies of galaxy images, which we make publicly available.11 This tool is largely based on the IDL code described in Lotz et al. (2004, 2006, 2008a,b) for”
THE PERSISTENCE OF COOL GALACTIC WINDS IN HIGH STELLAR MASS GALAXIES BETWEEN z ∼ 1.4 AND ∼1 (2009, methodology): “These are nonparametric measurements described in Lotz et al. (2004, 2006).”
Early and Rapid Merging as a Formation Mechanism of Massive Galaxies: Empirical Constraints (2005, methodology): “Merger Fractions at z > 1 Merger fractions at z > 1.2 are currently all determined through morphological methods (Conselice et al. 2003a; Lotz et al. 2004).”
Virgo Cluster Early-Type Dwarf Galaxies with the Sloan Digital Sky Survey. III. Subpopulations: Distributions, Shapes, Origins (2007, methodology): “…then compute the parameters defining an elliptical aperture (axial ratio and position angle) from the image moments (Abraham et al. 1994), and derive a “Petrosian semimajor axis” ap, i.e., we use ellipses instead of circles in the calculation of the Petrosian radius (see, e.g., Lotz et al. 2004a).”
The Rest-Frame Far-Ultraviolet Morphologies of Star-Forming Galaxies at z ~ 1.5 and 4 (2006, background): “Finally,morphologymeasures such as rotational asymmetry and clumpiness, which involve subtracting images and/or a correction for the background noise signal, are less robust at low signal-to-noise (S/N) levels (Lotz et al. 2004).”
THE IMPACT OF INTERACTIONS, BARS, BULGES, AND ACTIVE GALACTIC NUCLEI ON STAR FORMATION EFFICIENCY IN LOCAL MASSIVE GALAXIES (2012, methodology): “First, we use a set of quantitative morphological parameters measured by Wang et al. (2011) for the GASS sample, following the technique of Lotz et al. (2004).”
MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, neutral): “Second, we consider morphologically-selected mergers, identified on the basis of by-eye classification or automated morphological criteria such as the concentration-asymmetry (CAS) or Gini-M20 planes (see e.g. Conselice et al. 2003; Lotz et al. 2004).”
The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1 (2009, methodology): “To test the consistency of the measured parameters, these quantities have been computed using two independent morphological analysis codes adopting a “quasi-Petrosian” image thresholding technique (Abraham et al. 2007) and a Petrosian aperture (Lotz et al. 2004; Cassata et al. 2007).”
Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, methodology): “We measure non-parametric morphologies by using code originally developed for idealized merger simulations (Lotz et al. 2008a, 2010a,b) and also applied to galaxy surveys (Lotz et al. 2004, 2008b, 2011).”
GALAXY STELLAR MASS ASSEMBLY BETWEEN 0.2 < z < 2 FROM THE S-COSMOS SURVEY (2009, neutral): “This classification includes Gini, Concentration, Asymmetry, and M20 (e.g. Lotz et al. 2004).”
Deep GALEX Imaging of the COSMOS HST Field: A First Look at the Morphology of z ~ 0.7 Star-forming Galaxies (2007, methodology): “Lotz et al. (2004) use the isophote of surface brightness µ = µ(rpetro) on a smoothed version of the image, the smoothing kernel being a gaussian of σ = 0.2 × rpetro, as the boundary of their galaxies.”