Three‐dimensional Simulations of Inflows Irradiated by a Precessing Accretion Disk in Active Galactic Nuclei: Formation of Outflows

Abstract

We present three-dimensional hydrodynamical simulations of gas flows in the vicinity of an active galactic nucleus (AGN) powered by a precessing accretion disk. We consider the effects of the radiation force from such a disk on its environment on a relatively large scale (up to ~10 pc). We implicitly include the precessing disk by forcing the disk radiation field to precess around a symmetry axis with a given period (P) and a tilt angle (?). We study the time evolution of the flows irradiated by the disk and investigate basic dependencies of the flow morphology, mass flux, and angular momentum on different combinations of ? and P. As this is our first attempt to model such three-dimensional gas flows, we consider a simplest form of radiation force, i.e., force due to electron scattering, and neglect the forces due to line and dust scattering/absorption. Furthermore, the gas is assumed to be nearly isothermal. We find that the gas flow settles into a configuration with two components, (1) an equatorial inflow and (2) a bipolar inflow/outflow, with the outflow leaving the system along the poles (the directions of disk normals). However, the flow does not always reach a steady state. We find that the maximum outflow velocity and the kinetic outflow power at the outer boundary can be reduced significantly with increasing ?. We also find that the mass inflow rate across the inner boundary does not change significantly with increasing ?. The amount of the density-weighted mean specific angular momentum deposited in the environment by the precessing disk increases as P approaches the gas free-fall time (tff) and then decreases as P becomes much larger than tff. Generally, the characteristics of the flows are closely related to a combination of P and ?, but not to P and ? individually. Our models exhibit helical structures in the weakly collimated outflows. Although on different scales, the model reproduces the $t{Z}$ -->- or $t{S}$ -->-shaped density morphology of gas outflows, which are often seen in radio observations of AGNs.