Size Functions In Galaxy Morphology Classification

This paper introduces the concept of size functions in galaxy morphology classification, which are geometrical-topological shape descriptors which can be tailor-made to describe the shapes of objects of interest. For the three main classes of galaxies obtained from the Hubble classification scheme, namely, elliptical, spiral and lenticular, the size functions are obtained from two sets of measuring functions based on shape and pixel intensities. For elliptical galaxies, the ellipticity is considered for the shape measuring function whereas for spiral galaxies the pitch angle at turnover for the spiral arms is used. For lenticular galaxies the shape is obtained from eccentricity considerations. The intensity measuring functions can be obtained after color segmentation using an Otsu based method. Use of size functions is useful for automating the galaxy classification, as the methodology is robust and allows flexibility. Initial results are promising.