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

Kalinova, V.; Colombo, D.; Rosolowsky, E.; Kannan, R.; Galbany, L.; García-Benito, R.; González Delgado, R.; Sánchez, S. F.; Ruiz-Lara, T.; Méndez-Abreu, J.; Catalán-Torrecilla, C.; Sánchez-Menguiano, L.; de Lorenzo-Cáceres, A.; Costantin, L.; Florido, E.; Kodaira, K.; Marino, R. A.; Läsker, R.; Bland-Hawthorn, J.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 469, Issue 3, p.2539-2594

Advertised on:
8
2017
Number of authors
19
IAC number of authors
1
Citations
35
Refereed citations
33
Description
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}=√{V^2+σ ^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, fd = 1 - M*/Mdyn, have the largest value for SR and SP classes (˜ 74 per cent and ˜ 71 per cent, respectively) in contrast to the FL and RP classes (with ˜ 59 per cent and ˜ 61 per cent, respectively). Circular curve classification presents an alternative to typical morphological classification and appears more tightly linked to galaxy evolution.
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