2009ApJ...693.1929K

We study the axisymmetric and nonaxisymmetric, time-dependent hydrodynamics of gas that is under the influence of the gravity of a supermassive black hole (SMBH) and the radiation force produced by a radiatively efficient flow accreting onto the SMBH. We have considered two cases: (1) the formation of an outflow from the accretion of the ambient gas without rotation and (2) that with weak rotation. The main goals of this study are (1) to examine if there is a significant difference between the models with identical initial and boundary conditions but in different dimensionality (two and three dimensions) and (2) to understand the gas dynamics in active galactic nuclei. Our three-dimensional simulations of a nonrotating gas show small yet noticeable nonaxisymmetric small-scale features inside the outflow. The outflow as a whole and the inflow do not seem to suffer from any large-scale instability. In the rotating case, the nonaxisymmetric features are very prominent, especially in the outflow which consists of many cold dense clouds entrained in a smoother hot flow. The three-dimensional outflow is nonaxisymmetric due to the shear and thermal instabilities. In both two- and three-dimensional simulations, gas rotation increases the outflow thermal energy flux, but reduces the outflow mass and kinetic energy fluxes. Rotation also leads to time variability and fragmentation of the outflow in the radial and latitudinal directions. The collimation of the outflow is reduced in the models with gas rotation. The time variability in the mass and energy fluxes is reduced in the three-dimensional case because of the outflow fragmentation in the azimuthal direction. The virial mass estimated from the kinematics of the dense cold clouds found in our three-dimensional simulations of rotating gas underestimates the actual mass used in the simulations by about 40%. The opening angles (∼30°) of the bi-conic outflows found in the models with rotating gas are very similar to that of the nearby Seyfert galaxy NGC 4151 (∼33°). The radial velocities of the dense cold clouds from the simulations are compared with the observed gas kinematics of the narrow-line region of NGC 4151.