The (black hole mass)-(host spheroid luminosity) 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 M_(bh), we derive the M_(bh)-(host spheroid luminosity, L) relation for (i) the subsample of 24 core-Sersic galaxies with partially depleted cores, and (ii) the remaining subsample of 48 Sersic galaxies. Using (K_s)-band 2MASS data, we find the near-linear relation M_(bh) ~ L_(K_s)^(1.10+/-0.20) for the core-Sersic spheroids thought to be built in additive dry merger events, while M_(bh) ~ L_(K_s)^(2.73+/-0.55) 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)-sigma 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_sph mass ratio of ~0.2%, we advocate that the near-linear M_bh-L and M_bh-M_sph relations observed at high masses may have instead largely arisen 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 AGN, finding many masses between that of stellar mass black holes and supermassive black holes. 
Alister W. Graham and Nicholas Scott
astro-ph.CO