Innermost structure and near-infrared radiation of dusty clumpy tori in active galactic nuclei

TL;DR

This paper models the innermost structure of dusty tori in active galactic nuclei, explaining observed near-infrared radii discrepancies by considering anisotropic illumination and viewing angles, and discusses future X-ray spectroscopy insights.

Contribution

It introduces a model incorporating anisotropic disk illumination to resolve the systematic discrepancy in dust sublimation radii in AGN tori.

Findings

Anisotropic illumination explains the smaller observed NIR radii.

Viewing angle causes scatter in NIR time delays.

Future high-resolution X-ray spectroscopy will reveal clump dynamics.

Abstract

The dusty clumpy torus surrounds the central black hole (BH) and the accretion disk in active galactic nuclei, and governs the growth of super-massive BHs via gas fueling towards the central engine. Near-infrared (NIR) monitoring observations have revealed that the torus inner radius is determined by the dust sublimation process. However, the observed radii are systematically smaller than the theoretical predictions by a factor of three. We take into account the anisotropic illumination by the central accretion disk to the torus, and calculate the innermost structure of the torus and the NIR time variablity. We then show that the anisotropy naturally solves the systematic descrepancy and that the viewing angle is the primary source to produce an object-to-object scatter of the NIR time delay. Dynamics of clumps at the innermost region of the torus will be unveiled via future high-resolution X-ray spectroscopy (e.g., Astro-H).