Towards a new classification of galaxies: principal component analysis of CALIFA circular velocity curves

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We present a galaxy classification system for 238 (E1-Sdm) CALIFA (Calar Alto Legacy Integral Field Area) galaxies based on the shapes and amplitudes of their circular velocity curves (CVCs). We infer the CVCs from the de-projected surface brightness of the galaxies, after scaling by a constant mass-to-light ratio based on stellar dynamics - solving axisymmetric Jeans equations via fitting the second velocity moment V-rms = root V-2 + sigma(2) of the stellar kinematics. We use principal component analysis (PCA) applied to the CVC shapes to find characteristic features and use a k-means classifier to separate circular curves into classes. This objective classification method identifies four different classes, which we name slow-rising (SR), flat (FL), round-peaked (RP) and sharp-peaked (SP) circular curves. SR are typical for low-mass, late-type (Sb-Sdm), young, faint, metal-poor and disc-dominated galaxies. SP are typical for high-mass, early-type (E1-E7), old, bright, metal-rich and bulge-dominated galaxies. FL and RP appear presented by galaxies with intermediate mass, age, luminosity, metallicity, bulge-to-disc ratio and morphologies (E4-S0a, Sa-Sbc). The discrepancy mass factor, f(d) = 1 - M-*/M-dyn, have the largest value for SR and SP classes (similar to 74 per cent and similar to 71 per cent, respectively) in contrast to the FL and RP classes (with similar to 59 per cent and similar to 61 per cent, respectively). Circular curve classification presents an alternative to typical morphological classification and appears more tightly linked to galaxy evolution.
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Artículo firmado por 19 autores. We are grateful to the anonymous referees for their constructive comments, which helped us to substantially improve the manuscript. VK acknowledges Glenn van de Ven, Jesus Falcón Barroso and Mariya Lyubenova for the relevant discussions. VK is supported by the Avadh Bhatia Fellowship at the University of Alberta. VK, DC and ER are supported by a Discovery Grant from NSERC of Canada. DC acknowledges support by the Deutsche Forschungsgemeinschaft, DFG through project number SFB956C. LG is supported in part by the US National Science Foundation under Grant AST-1311862. LSM thanks support from the Spanish Ministerio de Economía y Competitividad (MINECO) via grant AYA2012-31935. RGD and RGB are supported by the Spanish Ministerio de 31 Ciencia e Innovación under grant AYA2010-15081 and AyA2014-57490-P. SFS thanks the CONACYT-125180 and DGAPA-IA100815 projects for providing him support in this study. EF acknowledges support from MINECO and JA grants, AYA2014-53506- P and FQM-108. RAM acknowledges support by the Swiss National Science Foundation. JM-A acknowledges support from the European Research Council Starting Grant (SEDMorph; PI: V. Wild).; This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration; Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the US Department of Energy Office of Science and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS website is; SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofisica de Canarias, the Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut fur Astrophysik Potsdam (AIP), Max-Planck-Institut fur Astronomie (MPIA Heidelberg), Max-Planck-Institut fur Astrophysik (MPA Garching), Max-Planck-Institut fur Extraterrestrische Physik (MPE), National Astronomical Observatory of China, New Mexico State University, New York University, University of Notre Dame, Observatario Nacional/MCTI, the Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autonoma de Mexico, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University and Yale University.
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