On the Linearity of the Black Hole–Bulge Mass Relation in Active and in Nearby Galaxies

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Abstract
Analysis of (Palomar-Green) PG quasar observations suggests a nonlinear relation between the black hole mass, MBH, and the bulge mass, Mbulge, although a linear relation, as proposed for nearby galaxies, cannot be ruled out. New MBH values for nearby galaxies from K. Gebhardt et al., and Lbulge 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 MBH-Mbulge relation. The combined sample of 40 active and nonactive galaxies suggests a significantly nonlinear relation, MBH ∝ M. Further support for a nonlinear relation is provided by the slope of the MBH-stellar velocity dispersion relation found recently, and by the low MBH found in late-type spiral galaxies. The mean MBH/Mbulge ratio is therefore not a universal constant, but rather drops from ~0.5% in bright (MV ~ -22) ellipticals to ~0.05% in low-luminosity (MV ~ -18) bulges. Hubble Space Telescope determinations of MBH in late-type spirals, and of the bulge magnitude in narrow-line Seyfert 1 galaxies (both predicted to have low MBH), can further test the validity of the nonlinear MBH-Mbulge relation.
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