MORFOMETRYKA—A NEW WAY OF ESTABLISHING MORPHOLOGICAL CLASSIFICATION OF GALAXIES

Abstract

We present an extended morphometric system to automatically classify galaxies from astronomical images. The new system includes the original and modified versions of the CASGM coefficients (Concentration C1, Asymmetry A3, and Smoothness S3), and the new parameters entropy, H, and spirality σψ. The new parameters A3, S3, and H are better to discriminate galaxy classes than A1, S1, and G, respectively. The new parameter σψ captures the amount of non-radial pattern on the image and is almost linearly dependent on T-type. Using a sample of spiral and elliptical galaxies from the Galaxy Zoo project as a training set, we employed the Linear Discriminant Analysis (LDA) technique to classify EFIGI (Baillard et al. 4458 galaxies), Nair & Abraham (14,123 galaxies), and SDSS Legacy (779,235 galaxies) samples. The cross-validation test shows that we can achieve an accuracy of more than 90% with our classification scheme. Therefore, we are able to define a plane in the morphometric parameter space that separates the elliptical and spiral classes with a mismatch between classes smaller than 10%. We use the distance to this plane as a morphometric index (Mi) and we show that it follows the human based T-type index very closely. We calculate morphometric index Mi for ∼780k galaxies from SDSS Legacy Survey–DR7. We discuss how Mi correlates with stellar population parameters obtained using the spectra available from SDSS–DR7.