Morphological classification of nearby galaxies based on asymmetry and luminosity concentration

Abstract

We investigate the behaviour of the asymmetry parameter A as a morphological parameter using a `volume-limited' sample of 349 galaxies (distance <=25Mpc,M_V<=-18.5mag) and a larger magnitude-limited sample of 707 nearby galaxies. We confirm the correlation of A with morphological type. The late-type galaxies (Sdm, Sm and Im) have larger A than early-type galaxies, and they tend to have larger A than spiral galaxies. We investigate the usefulness of the A versus concentration index C_in diagram as a tool for the regular-irregular and early-late classification. The diagram is not very useful to the regular versus late-type irregular classification, as inferred previously, but it is found to be useful to the early-late classification.