Systematics of bulge-to-disk ratios

Abstract

Decompositions of the blue-band luminosity profiles of 98 galaxies into spheroidal and disk components on a homogeneous system are used to study the systematics of bulge-to-disk ratios and related parameters. The mean fractional luminosity of the spheroidal component is found to be a monotonically decreasing function of stage along the revised Hubble sequence from early-type lenticulars to late-type spirals. The data give no support to the suggestion that lenticulars form a gas-poor sequence of disk systems parallel to the gas-rich spiral sequence. The variations along the Hubble sequence of the mean absolute magnitudes, effective radii, and effective specific intensities of the spheroidal and disk components show that on average the spheroids of lenticular galaxies are systematically smaller and denser, but fainter in total luminosity, than elliptical galaxies. However, both ellipticals and the spheroidal components of lenticulars obey the same effective radius-surface brightness relation.