Authors: Alister W. Graham & Nicholas Scott
Abstract:From a sample of 72 galaxies with reliable supermassive black hole masses Mbh, we derive the Mbh—(host spheroid luminosity, L) relation for i) the subsample of 24 core-Sérsic galaxies with partially depleted cores, and ii) the remaining subsample of 48 Sérsic galaxies. Using Ks-band Two Micron All Sky Survey data, we find the near-linear relation Mbh ∝ LK_s1.10±0.20 for the core-Sérsic spheroids thought to be built in additive dry merger events, while Mbh ∝ LK_s2.73±0.55 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 the near-linear `Magorrian relations' and 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 at high masses may have instead largely arisen from the simple, additive dry merging of galaxies, and that feedback results in a dramatically different scaling relation. We therefore introduce a new quadratic cold-gas 'quasar' mode feeding equation for semi-analytical models to reflect the quadratic mass 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, possibly having discovered the missing population between stellar mass and supermassive black holes.