Hypercubes of AGN Tori (HYPERCAT) -- II. Resolving the Torus with Extremely Large Telescopes

TL;DR

This paper demonstrates that next-generation 30-meter telescopes will resolve the dust structures around AGNs, enabling detailed imaging and analysis of the torus, which can break degeneracies in previous unresolved studies.

Contribution

It models the resolving capabilities of upcoming telescopes for AGN tori, including image recovery techniques and analysis of dust distribution and silicate features.

Findings

Resolved AGN torus structures show $S_{10}$ variations.

A dusty screen with $A_V > 9$ mag explains unresolved $S_{10}$ measurements.

Model fits suggest a highly inclined emission ring or a thin flared disk.

Abstract

Recent infrared interferometric observations revealed sub-parsec scale dust distributions around active galactic nuclei (AGNs). Using images of CLUMPY torus models and NGC 1068 as an example, we demonstrate that the near- and mid-infrared nuclear emission of some nearby AGNs will be resolvable in direct imaging with the next generation of 30~m telescopes, potentially breaking degeneracies from previous studies that used integrated spectral energy distributions of unresolved AGN tori. To that effect we model wavelength-dependent point spread functions from the pupil images of various telescopes: James Webb Space Telescope, Keck, Giant Magellan Telescope, Thirty Meter Telescope, and Extremely Large Telescope. We take into account detector pixel scales and noise, and apply deconvolution techniques for image recovery. We also model 2D maps of the 10-micron silicate feature strength, $S_{10}$, of NGC 1068 and compare with observations. When the torus is resolved, we find $S_{10}$ variations across the image. However, to reproduce the $S_{10}$ measurements of an unresolved torus a dusty screen of $A_V > 9$ mag is required. We also fit the first resolved image of the K-band emission in NGC 1068 recently published by the GRAVITY collaboration, deriving likely model parameters of the underlying dust distribution. We find that both 1) an elongated structure suggestive of a highly inclined emission ring, and 2) a geometrically thin but optically thick flared disk where the emission arises from a narrow strip of hot cloud surface layers on the far inner side of the torus funnel, can explain the observations.