Morphology Segregation of Galaxies in the Color-Color Gradient Space

Abstract

We have found the u -r color versus g -i color gradient space can be used for highly successful morphology classification of galaxies in the Sloan Digital Sky Survey. In this space galaxies form early and late type branches well-separated from each other. The location of galaxies along the branches reflects the degree and locality of star formation activity, and monotonically corresponds to the sequence of morphological subclasses. When the concentration index is used together, the completeness and reliability of classification reaches about 91% for a training set of SDSS galaxies brighter than r~15.9. At faintest magnitudes (r~17.5) of the SDSS spectroscopic sample, the performance still remains at about 88%. The new classification scheme will help us find accurate relations of galaxy morphology with spatial and temporal environments, and help one understand the origin of morphology of galaxies.