Low-density, radiatively inefficient rotating-accretion flow on to a black hole

We study low-density axisymmetric accretion flows on to black holes (BHs) with two-dimensional hydrodynamical simulations, adopting the a-viscosity prescription. When the gas angular momentum is low enough to form a rotationally supported disc within the Bondi radius (R-B), we find a global steady accretion solution. The solution consists of a rotational equilibrium distribution around r similar to R-B, where the density follows rho alpha (1+ R-B/r)(3/2), surrounding a geometrically thick and optically thin accretion disc at the centrifugal radius R-C(