Coevolution Between Supermassive Black Holes and Bulges Is Not Via
  Internal Feedback Regulation But By Rationed Gas Supply Due To Angular
  Momentum Distribution
  We reason that, without physical fine-tuning, neither the supermassive black
holes (SMBHs) nor the stellar bulges can self-regulate or inter-regulate by
driving away already fallen cold gas to produce the observed correlation
between them. We suggest an alternative scenario where the observed mass ratios
of the SMBHs to bulges reflect the angular momentum distribution of infallen
gas such that the mass reaching the stable accretion disc is a small fraction
of that reaching the bulge region, averaged over the cosmological time scales.
We test this scenario using high resolution, large-scale cosmological
hydrodynamic simulations (without AGN feedback), assuming the angular momentum
distribution of gas landing in the bulge region to yield a Mestel disc that is
supported by independent simulations resolving the Bondi radii of SMBHs. A mass
ratio of $0.1-0.3\%$ between the very low angular momentum gas that free-falls
to the sub-parsec region to accrete to the SMBH and the overall star formation
rate is found. This ratio is found to increase with increasing redshift to
within a factor of $\sim 2$, suggesting that the SMBH to bulge ratio is nearly
redshift independent, with a modest increase with redshift, a testable
prediction. Furthermore, the duty cycle of active galactic nuclei (AGN) with
high Eddington ratios is expected to increase significantly with redshift.
Finally, while SMBHs and bulges are found to coevolve on $\sim 30-150$Myr time
scales or longer, there is indication that, on shorer time scales, the SMBH
accretion rate and star formation may be less correlated.
