Transition of BH feeding from the quiescent regime into star-forming
  cold disk regime
  We study the properties of rotating accretion flows onto supermassive black
holes (SMBHs) using axisymmetric two-dimensional hydrodynamical simulations
with radiative cooling and BH feedback. The simulations resolve the accretion
dynamics of gas outside from the BH influence radius through an inner accretion
disk. For lower Bondi accretion rates in units of the Eddington rate
($\dot{M}_{\rm B}\ll 10^{-3}~\dot{M}_{\rm Edd}$), the BH feeding is suppressed
due to turbulent motion by several orders of magnitudes from the Bondi rate.
Thus, the radiative luminosity results in as low as $\sim
10^{-10}-10^{-7}~L_{\rm Edd}$, where $L_{\rm Edd}$ is the Eddington luminosity.
For higher rates of $\dot{M}_{\rm B}> 10^{-3}~\dot{M}_{\rm Edd}$, the
optically-thin accreting gas cools via free-free emission and forms a
geometrically-thin disk, which feeds the BH efficiently and increases the
radiative luminosity to $> 10^{-3}~L_{\rm Edd}$. The transitional behavior of
accreting BHs in galactic nuclei from radiatively inefficient phases to cold
disk accretion naturally explains (1) the reason for the offset between the
observed luminosities and theoretical predictions for nearby quiescent SMBHs,
and (2) the conditions to fuel gas into the nuclear SMBH. In addition, the cold
disk formed in galactic nuclei tends to be gravitationally unstable and leads
to star formation when the Bondi rate is as high as $ \dot{M}_{\rm B} >
10^{-2}~M_\odot~{\rm yr}^{-1}$. This is a plausible explanation of the
correlation observed between star formation rates and BH feeding rates in
Seyfert galaxies.
