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

Abstract

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 $V_{\mathrm{rms}}=\sqrt{V^2+{\sigma }^2}$ 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-disk ratio and morphologies (E4-S0a, Sa-Sbc). The discrepancy mass factor, $f_d=1-M_{\ast }/M_{dyn}$, have the largest value for SR and SP classes ($\sim$ 74 per cent and $\sim$ 71 per cent, respectively) in contrast to the FL and RP classes (with $\sim$ 59 per cent and $\sim$ 61 per cent, respectively). Circular curve classification presents an alternative to typical morphological classification and appears more tightly linked to galaxy evolution.

Accepted for publication in MNRAS (Minor changes), 123 pages, 19 figures, 87 Tables (containing the basic properties of the 238 E1-Sdm galaxies; the five main Principal Component Eigenvectors; the five main Principal Components - PC_i; the Multi-Gaussian Expansion models - MGEs; the circular velocity curve models and their uncertainties)

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• SDSS IV MaNGA: Bar pattern speed in Milky Way Analogue galaxies
• Morphological evolution and galactic sizes in the L-Galaxies SA model
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• Investigating the link between inner gravitational potential and star-formation quenching in CALIFA galaxies
• The GMRT archive atomic gas survey -- II. Mass modelling and dark matter halo properties across late-type spirals
• The SAMI Galaxy Survey: embedded discs and radial trends in outer dynamical support across the Hubble sequence
• Molecular Gas of the Most Massive Spiral Galaxies I: a Case Study of NGC 5908
• Forward modeling of galaxy kinematics in slitless spectroscopy
• A mass-velocity anisotropy relation in galactic stellar disks
• Local variations of the Stellar Velocity Ellipsoid-I: the disc of galaxies in the Auriga simulations
• MaNGA DynPop. VII. A Unified Bulge-Disk-Halo Model for Explaining Diversity in Circular Velocity Curves of 6000 Spiral and Early-Type Galaxies
• Rotation curves and dynamical masses of MaNGA barred galaxies
• Diverse Rotation Curves of Galaxies in a Simulated Universe: the Observed Dependence on Stellar Mass and Morphology Reproduced
• Spiral shocks induced in galactic gaseous disk: hydrodynamic understanding of observational properties of spiral galaxies
• Bridging Galaxy Dynamics and Baryon Efficiency of 40 EDGE-CALIFA galaxies
• Spatially-resolved analysis of neutral winds, stars and ionized gas kinematics with MEGARA/GTC: new insights on the nearby galaxy UGC 10205
• A bar stability criterion distinguishing between modified gravity and dark matter in galaxies
• The vertical structure of the stellar disk in NGC 551
• Radar-Chart Analysis of Star-Formation Quenching Stages Across Circular Velocity Curve Classes in Nearby CALIFA Galaxies