THE MBH–LSPHEROID RELATION AT HIGH AND LOW MASSES, THE QUADRATIC GROWTH OF BLACK HOLES, AND INTERMEDIATE-MASS BLACK HOLE CANDIDATES

From a sample of 72 galaxies with reliable supermassive black hole masses Mbh, we derive the Mbh–(host spheroid luminosity, L) relation for (1) the subsample of 24 core-Sérsic galaxies with partially depleted cores, and (2) the remaining subsample of 48 Sérsic galaxies. Using Ks-band Two Micron All Sky Survey data, we find the near-linear relation Mbh∝L1.10 ± 0.20Ks for the core-Sérsic spheroids thought to be built in additive dry merger events, while we find the relation Mbh∝L2.73 ± 0.55Ks for the Sérsic spheroids built from gas-rich processes. After converting literature B-band disk galaxy magnitudes into inclination- and dust-corrected bulge magnitudes, via a useful new equation presented herein, we obtain a similar result. Unlike with the Mbh–(velocity dispersion) diagram, which is also updated here using the same galaxy sample, it remains unknown whether barred and non-barred Sérsic galaxies are offset from each other in the Mbh–L diagram. While black hole feedback has typically been invoked to explain what was previously thought to be a nearly constant Mbh/MSpheroid mass ratio of ∼0.2%, we advocate that the near-linear Mbh–L and Mbh–MSpheroid relations observed at high masses may have instead arisen largely from the additive dry merging of galaxies. We argue that feedback results in a dramatically different scaling relation, such that black hole mass scales roughly quadratically with the spheroid mass in Sérsic galaxies. We therefore introduce a revised cold-gas “quasar” mode feeding equation for semi-analytical models to reflect what we dub the quadratic growth of black holes in Sérsic galaxies built amidst gas-rich processes. Finally, we use our new Sérsic Mbh–L equations to predict the masses of candidate intermediate mass black holes in almost 50 low-luminosity spheroids containing active galactic nuclei, finding many masses between that of stellar mass black holes and supermassive black holes.