On the large-scale outflows in active galactic nuclei: consequences of coupling the mass-supply rate and accretion luminosity

TL;DR

This study uses hydrodynamical simulations to explore how large-scale outflows in active galactic nuclei relate to accretion luminosity, revealing a strong correlation and conditions for super-Eddington accretion.

Contribution

It demonstrates the coupling between mass-supply rate and accretion luminosity in AGN outflows, highlighting the conditions for super-Eddington accretion and the geometry of inflows and outflows.

Findings

Mass-outflow rate scales with luminosity as a power law with index ~2.

Super-Eddington accretion occurs in the equatorial region under certain conditions.

Outflow geometry varies with temperature and luminosity, resembling stellar wind models.

Abstract

(Abridged) We present two-dimensional hydrodynamical simulations of slowly rotating gas that is under the influence of the gravity of a super massive black hole and is irradiated by a thin UV accretion disc and a spherical X-ray corona. We calculate the accretion luminosity of a system based on the accretion-rate which is assumed to be equal to the mass-supply rate at the radius of ~10^-2 pc. For the models with high temperature gas at large radii (~10 pc) and high luminosities, we find a strong correlation between the mass-outflow rate (Mdot_out) and the luminosity (L). The power law index (q) describing the Mdot_out-L relation is q=2.0(+/-0.1), which is very similar to that for radiation-driven stellar and disc wind models. More surprisingly, for high density at large radii, we find steady state solutions with the accretion luminosity exceeding the Eddington limit. The super-Eddington accretion proceeds in the equatorial region and is possible because the radiation flux from the disc is significantly reduced in the equatorial direction due to the geometrical foreshortening effect. In all models, an outflow is driven from an inflow with sub-Keplerian rotation. For high temperature at large radii, the inflow occurs over a wide range of the polar angles, and the outflow occurs in a relatively narrow polar cone. However, for the super-Eddington cases with low temperature at large radii, the inflow persists only very close to the equatorial plane, resembling a thin accretion disc, while the outflow arises in a wide range of radii and polar angles. The geometry of this extreme inflow-outflow solution is very similar to a radiation-driven wind from a luminous Keplerian accretion disc.