Spherical accretion in giant elliptical galaxies: multi-transonicity,
  shocks, and implications on AGN feedback
  Isolated massive elliptical galaxies, or that are present at the center of
cool-core clusters, are believed to be powered by hot gas accretion directly
from their surrounding hot X-ray emitting gaseous medium. This leads to a giant
Bondi-type spherical/quasi-spherical accretion flow onto their host SMBHs, with
the accretion flow region extending well beyond the Bondi radius. In this work,
we present a detailed study of Bondi-type spherical flow in the context of
these massive ellipticals by incorporating the effect of entire gravitational
potential of the host galaxy in the presence of cosmological constant
$\Lambda$, considering a five-component galactic system (SMBH + stellar + dark
matter + hot gas + $\Lambda$). The current work is an extension of Ghosh \&
Banik (2015), who studied only the cosmological aspect of the problem. The
galactic contribution to the potential renders the (adiabatic) spherical flow
to become {\it multi-transonic} in nature, with the flow topology and flow
structure significantly deviating from that of classical Bondi solution. More
notably, corresponding to moderate to higher values of galactic mass-to-light
ratios, we obtain Rankine-Hugoniot shocks in spherical wind flows. Galactic
potential enhances the Bondi accretion rate. Our study reveals that there is a
strict lower limit of ambient temperature below which no Bondi accretion can be
triggered; which is as high as $\sim 9 \times 10^6 \, K$ for flows from hot
ISM-phase, indicating that the hot phase tightly regulates the fueling of host
nucleus. Our findings may have wider implications, particularly in the context
of outflow/jet dynamics, and radio-AGN feedback, associated with these massive
galaxies in the contemporary Universe.
