Spheroidal luminosities: A quantitative basis for the galaxian sequence

A quantitative one-dimensional scheme of galaxy classification is proposed based on the luminosity of the spheroidal component Lsph. After noting previous work showing the correlations between color, velocity dispersion, scale, metallicity, and degree of rotational support with Lsph, the authors show that the Hubble type correlates as well. The authors find that (in terms of blue magnitudes, with H0 = 100 km/s/Mpc), if Msph < -20 the system is almost always an elliptical, if -20 < Msph < -17 comparable frequencies of elliptical, S0, and spirals are found, and if -17 < Msph < -16 the systems are typically spiral or irregular. Due to incompleteness of the observational data, little conclusive can be said about systems with Msph > -16.