The m bh-l spheroid relation at high and low masses, the quadratic growth of black holes, and intermediate-mass black hole candidates

TLDR: In this article, the authors show that feedback results in a dramatically different scaling relation, such that black hole mass scales roughly quadratically with the spheroid mass in Sersic galaxies.

Abstract: From a sample of 72 galaxies with reliable supermassive black hole masses M bh, we derive the M bh-(host spheroid luminosity, L) relation for (1) the subsample of 24 core-Sersic galaxies with partially depleted cores, and (2) the remaining subsample of 48 Sersic galaxies. Using Ks -band Two Micron All Sky Survey data, we find the near-linear relation M bh∝L 1.10 ± 0.20 Ks for the core-Sersic spheroids thought to be built in additive dry merger events, while we find the relation M bh∝L 2.73 ± 0.55 Ks for the Sersic 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 M bh-(velocity dispersion) diagram, which is also updated here using the same galaxy sample, it remains unknown whether barred and non-barred Sersic galaxies are offset from each other in the M bh-L diagram. While black hole feedback has typically been invoked to explain what was previously thought to be a nearly constant M bh/M Spheroid mass ratio of ~0.2%, we advocate that the near-linear M bh-L and M bh-M Spheroid 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 Sersic 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 Sersic galaxies built amidst gas-rich processes. Finally, we use our new Sersic M bh-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.