Three-Dimensional Simulations of Dynamics of Accretion Flows Irradiated by a Quasar

Abstract

We study the axisymmetric and non-axisymmetric, time-dependent hydrodynamics of gas that is under the influence of the gravity of a super massive 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 (2-D and 3-D), and (2) to understand the gas dynamics in AGN. Our 3-D simulations of a non-rotating gas show small yet noticeable non-axisymmetric 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 non-axisymmetric features are very prominent, especially in the outflow which consists of many cold dense clouds entrained in a smoother hot flow. The 3-D outflow is non-axisymmetric due to the shear and thermal instabilities. In both 2-D and 3-D 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 3-D 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 3-D simulations of rotating gas underestimates the actual mass used in the simulations by about 40 %. (Abbreviated)