Geometrically thick obscuration by radiation-driven outflow from magnetized tori of active galactic nuclei

TL;DR

This study uses advanced radiative magnetohydrodynamics simulations to demonstrate how radiation-driven outflows from magnetized tori in active galactic nuclei create geometrically thick obscuration, aligning with observational data.

Contribution

It presents the first self-consistent simulation of IR and UV radiative transfer with MHD to model AGN obscuration without approximations, revealing steady-state torus dynamics.

Findings

The torus reaches a quasi-steady state with slow evolution.

Outflows are launched by UV radiation and driven by IR radiation.

Obscuration covers three-quarters of solid angle, matching observations.

Abstract

Near-Eddington radiation from active galactic nuclei (AGNs) has significant dynamical influence on the surrounding dusty gas, plausibly furnishing AGNs with geometrically thick obscuration. We investigate this paradigm with radiative magnetohydrodynamics simulations. The simulations solve the magnetohydrodynamics equations simultaneously with the infrared (IR) and ultraviolet (UV) radiative transfer (RT) equations; no approximate closure is used for RT. We find that our torus, when given a suitable sub-Keplerian angular momentum profile, spontaneously evolves toward a state in which its opening angle, density distribution, and flow pattern change only slowly. This "steady" state lasts for as long as there is gas resupply toward the inner edge. The torus is best described as a mid-plane inflow and a high-latitude outflow. The outflow is launched from the torus inner edge by UV radiation and expands in solid angle as it ascends; IR radiation continues to drive the wide-angle outflow outside the central hole. The dusty outflow obscures the central source in soft X-rays, the IR, and the UV over three quarters of solid angle, and each decade in column density covers roughly equal solid angle around the central source; these obscuration properties are similar to what observations imply.

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