On the linearity of the black hole-bulge mass relation in active and in nearby galaxies

Analysis of (Palomar-Green) PG quasar observations suggests a nonlinear relation between the black hole mass, M-BH, and the bulge mass, M-bulge, although a linear relation, as proposed for nearby galaxies, cannot be ruled out. New M-BH values for nearby galaxies from K. Gebhardt et al., and L-bulge measurements for Seyfert 1 galaxies from S. N. Virani et al., are used here to obtain a more accurate value for the slope of the M-BH-M-bulge relation. The combined sample of 40 active and nonactive galaxies suggests a significantly nonlinear relation, M-BH proportional to M-bulge(1.53 +/-0.14). Further support for a nonlinear relation is provided by the slope of the M-BH-stellar velocity dispersion relation found recently, and by the low M-BH found in late-type spiral galaxies. The mean M-BH/M-bulge ratio is therefore not a universal constant, but rather drops from similar to0.5% in bright (M-v similar to -22) ellipticals to similar to0.05% in low-luminosity (Mv similar to -18) bulges. Hubble Space Telescope determinations of M-BH in late-type spirals, and of the bulge magnitude in narrow-line Seyfert 1 galaxies (both predicted to have low M-BH), can further test the validity of the nonlinear M-BH-M-bulge relation.