The relative contributions of bulge and disk to the luminosity density of the universe

The authors have obtained redshifts for a virtually complete, magnitude-limited sample of galaxies in a set of randomly chosen fields. They use these in conjunction with previously measured bulge-to-disk ratios to determine the dependence of blue bulge-to-disk ratio on absolute magnitude, and the relative contributions of bulge and disk to the mean luminosity density of the universe. Through there is considerable scatter in bulge-to-disk ratio at all absolute magnitudes, the authors find that B/D varies as 0.61 (L/L*)0.28. When the different mass-to-light ratios of bulge and disk are taken into account, they find that roughly equal amounts of mass are incorporated in bulges and disks.