Time-resolved infrared emission from radiation-driven central obscuring structures in Active Galactic Nuclei

TL;DR

This paper presents a novel, time-resolved model of the obscuring structures in Active Galactic Nuclei, revealing wavelength-dependent morphology and variability driven by radiation pressure and X-ray heating.

Contribution

It introduces the first time-resolved spectral energy distributions and images for a physical model of AGN obscurers, incorporating hydrodynamics and radiative transfer.

Findings

Temporal changes are most visible at shorter wavelengths.

Mid-infrared images show elongated outflow cones.

Long wavelength emission is dominated by the dense disc.

Abstract

The central engines of Seyfert galaxies are thought to be enshrouded by geometrically thick gas and dust structures. In this article, we derive observable properties for a self-consistent model of such toroidal gas and dust distributions, where the geometrical thickness is achieved and maintained with the help of X-ray heating and radiation pressure due to the central engine. Spectral energy distributions (SEDs) and images are obtained with the help of dust continuum radiative transfer calculations with RADMC-3D. For the first time, we are able to present time-resolved SEDs and images for a physical model of the central obscurer. Temporal changes are mostly visible at shorter wavelengths, close to the combined peak of the dust opacity as well as the central source spectrum and are caused by variations in the column densities of the generated outflow. Due to the three-component morphology of the hydrodynamical models -- a thin disc with high density filaments, a surrounding fluffy component (the obscurer) and a low density outflow along the rotation axis -- we find dramatic differences depending on wavelength: whereas the mid-infrared images are dominated by the elongated appearance of the outflow cone, the long wavelength emission is mainly given by the cold and dense disc component. Overall, we find good agreement with observed characteristics, especially for those models, which show clear outflow cones in combination with a geometrically thick distribution of gas and dust, as well as a geometrically thin, but high column density disc in the equatorial plane.