Multiphase Gas Nature in the Sub-parsec Region of the Active Galactic Nuclei. III. Eddington Ratio Dependence on the Structures of Dusty and Dust-free Outflows

TL;DR

This study uses radiation hydrodynamics simulations to explore how the Eddington ratio influences the structure and dynamics of dusty and dust-free outflows in active galactic nuclei, revealing key dependencies on dust sublimation and outflow velocity.

Contribution

It provides new analytical and numerical insights into the Eddington ratio's role in shaping sub-parsec outflows and their observable obscuring fractions in AGNs.

Findings

Higher Eddington ratios lead to stronger outflows and larger dust sublimation radii.

Radial distributions of outflows are well described by steady spherical wind solutions.

Dust sublimation radius critically determines terminal velocity and column density.

Abstract

We investigated the influence of the Eddington ratio on sub-parsec-scale outflows in active galactic nuclei (AGNs) with supermassive black holes (SMBHs) masses of $10^7$ M$_{\odot}$ using two-dimensional radiation hydrodynamics simulations. When the range of Eddington ratio, $\gamma_{\rm Edd} > 10^{-3}$, the radiation force exceeds the gas pressure, leading to stronger outflows and larger dust sublimation radius. Although the sub-parsec-scale outflows is a time-dependence phenomena, our simulations demonstrated that the radial distributions can be well explained by the steady solutions of the spherically symmetric stellar winds. The dynamic structure of sub-parsec-scale outflows is influenced by the dust sublimation radius and the critical radii determined by the dynamical equilibrium condition. Although significantly affecting the outflow velocity, the Eddington ratio exerts minimal effects on temperature and number density distribution. Furthermore, our analytical solutions highlight the importance of the dust sublimation scale as a crucial determinant of terminal velocity and column density in dusty outflows. Through comparisons of our numerical model with the obscuring fraction observed in nearby AGNs, we revealed insights into the Eddington ratio dependence and the tendency towards the large obscuring fraction of the dusty and dust-free gases. The analytical solutions are expected to facilitate an understanding of the dynamical structure and radiation structures along the line of sight and their viewing angles from observations of ionized outflows.