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For refcode 2000AJ....119.2645B:
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2000AJ....119.2645B STRUCTURAL AND PHOTOMETRIC CLASSIFICATION OF GALAXIES. I. CALIBRATION BASED ON A NEARBY GALAXY SAMPLE MATTHEW A. BERSHADY Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706; mab@astro.wisc.edu ANNA JANGREN Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802; jangren@astro.psu.edu AND CHRISTOPHER J. CONSELICE Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706; chris@astro.wisc.edu Received 1999 August 30; accepted 2000 February 11 ABSTRACT 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. Key words: galaxies: compact-galaxies: fundamental parameters -galaxies: starburst
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