Structural and Photometric Classification of Galaxies. I. Calibration Based on a Nearby Galaxy Sample

By M. Bershady, A. Jangren, Christopher J. Conselice. 2000

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In this paper we define an observationally robust, multiparameter space for the classification of nearby and distant galaxies. The parameters include luminosity, color, and the image-structure parameters: size, image concentration, asymmetry, and surface brightness. Based on an initial calibration of this parameter space using the "normal" Hubble types surveyed in 1996 by Frei et al., we find that only a subset of the parameters provide useful classification boundaries for this sample. Interestingly, this subset does not include distance-dependent scale parameters such as size or luminosity. The essential ingredient is the combination of a spectral index (e.g., color) with parameters of image structure and scale: concentration, asymmetry, and surface brightness. We refer to the image structure parameters (concentration and asymmetry) as indices of "form." We define a preliminary classification based on spectral index, form, and surface brightness (a scale) that successfully separates normal galaxies into three classes. We intentionally identify these classes with the familiar labels of early, intermediate, and late. This classification, or others based on the above four parameters, can be used reliably to define comparable samples over a broad range in redshift. The size and luminosity distribution of such samples will not be biased by this selection process except through astrophysical correlations between spectral index, form, and surface brightness.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/25dfc4cb222de10bdb8192ee7ef06a13a4628132

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Citations in the corpus

The Evolution of Galaxy Structure Over Cosmic Time (2014, methodology): “…of measuring the radius is much less influenced by surface brightness dimming than other methods such as using an isophotal radius, and is therefore useful for measuring the same physical parts of galaxies at different redshifts (e.g., Petrosian 1976; Bershady et al. 2000; Graham et al. 2005).”
Near-Infrared Bright Galaxies at z ≃ 2. Entering the Spheroid Formation Epoch? (2003, methodology): “We measured theCASparameters (Conselice 2003; Bershady et al. 2000; and references therein), finding relatively high clumpiness (S), high asymmetry (A) and very low concentration (C) (see Table 1).”
COSMOS Morphological Classification with the Zurich Estimator of Structural Types (ZEST) and the Evolution Since z = 1 of the Luminosity Function of Early, Disk, and Irregular Galaxies (2006, methodology): “Frei’s galaxies span Hubble types from Ellipticals (T = −5) to Sd (T = 10); they have been used as a z = 0 benchmark for assessing galaxy morphologies at higher redshifts in a number of other works (e.g. Bershady et al. 2000; Simard et al. 2002; Lotz, Primack & Madau 2004).”
A New Nonparametric Approach to Galaxy Morphological Classification (2003, methodology): “We adopt the Bershady et al. (2000) definition as the ratio of the circular radii containing 20% and 80% of the “total flux” : C = 5 log10 ( r80 r20 ) (9) where r80 and r20 are the circular apertures containing 80% and 20% of the total flux, respectively.”
The Physical Nature of Rest-UV Galaxy Morphology during the Peak Epoch of Galaxy Formation (2006, unknown): “The “CAS” system of parameters has recently been a popular choice, characterizing galaxies on the basis of their concentration (C; Kent 1985, Bershady et al. 2000), asymmetry (A, Schade et al. 1995), and clumpiness (S, Conselice et al. 2003).”
Galaxy merger morphologies and time-scales from simulations of equal-mass gas-rich disc mergers (2008, methodology): “We adopt the Bershady et al. (2000) definition as the ratio of the circular radii containing 20% and 80% of the “total flux” : C = 5 log10 ( r80 r20 ) (2) where r80 and r20 are the circular apertures containing 80% and 20% of the total flux, respectively.”
Total Galaxy Magnitudes and Effective Radii from Petrosian Magnitudes and Radii (2005, methodology): “%) of the flux within the Petrosian aperture (Bershady et al. 2000).”
HISTORY OF GALAXY INTERACTIONS AND THEIR IMPACT ON STAR FORMATION OVER THE LAST 7 Gyr FROM GEMS (2009, methodology): “The CAS concentration index C (Bershady et al. 2000) is proportional to the logarithm of the ratio of the 80% to 20% curve of growth radii within 1.5 times the Petrosian inverted radius at r(η = 0.2), normalized by a logarithm C = 5 × log(r80%/r20”
The fundamental properties of galaxies and a new galaxy classification system (2006, methodology): “Modern studies have attempted to classify ellipticals by their structures (Kormendy & Bender 1996), and at using interacting and star formation properties to classify all galaxies (e.g., Conselice 1997; Conselice et al. 2000a; Conselice et al. 2000b; Bershady et al. 2000).”
Early and Rapid Merging as a Formation Mechanism of Massive Galaxies: Empirical Constraints (2005, background): “A minor merger is between systems with a mass ratio higher than 1:3. method for determining Nm, and the tabulated values, are discussed in Conselice et al. (2000a,b), Bershady et al. (2000), Conselice (2003b) and Conselice et al. (2003a).”
The structures of distant galaxies – III. The merger history of over 20 000 massive galaxies at z < 1.2 (2008, methodology): “For more detail see Bershady et al. (2000), Conselice et al. (2000), Conselice (2003), and Lotz et al. (2008).”
The Hubble Deep Field North SCUBA Super-map - III. Optical and near-infrared properties of submillimetre galaxies (2005, background): “The concentration index measur s the ratio of the amount of light at the radii that contain 80% and 20% of the total amount of light (Bershady et al. 2000).”
The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories (2003, background): “Brie y,ellipticalgalaxiesare the m ost concentrated system s,and the concentration ofstellar light decreases for later Hubble types (e.g., Bershady et al. 2000).”
THE DISKMASS SURVEY. I. OVERVIEW (2010, methodology): “Given the limited quality, depth, and dynamic range of the DSS data we did not pursue a quantitative classification (e.g., Bershady et al. 2000), but instead used these measurements to estimate disk central surface-brightness, scale-length, and ellipticity.”
Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, methodology): “We compute the concentration parameter C (Bershady et al. 2000): C = 5 log10 r80 r20 , (1) where r80 and r20 are circular apertures containing 80% and 20% of the total flux within the ellipse with semi-major axis 1.5rp (Conselice et al. 2003) of the galaxy center defined by minimizing the Asymmetry…”