Hypercubes of AGN Tori (HYPERCAT) – I. Models and Image Morphology

Abstract

Near- and mid-infrared interferometers have resolved the dusty parsec-scale obscurer (torus) around nearby active galactic nuclei (AGNs). With the arrival of extremely large single-aperture telescopes, the emission morphology will soon be resolvable unambiguously, without modeling directly the underlying brightness distribution probed by interferometers today. Simulations must instead deliver the projected 2D brightness distribution as a result of radiative transfer through a 3D distribution of dusty matter around the AGN. We employ such physically motivated 3D dust distributions in tori around AGNs to compute 2D images of the emergent thermal emission, using Clumpy, a dust radiative transfer code for clumpy media. We demonstrate that Clumpy models can exhibit morphologies with significant polar elongation in the mid-infrared (i.e. the emission extends perpendicular to the dust distribution) on scales of several parsecs, in line with observations in several nearby AGNs. We characterize the emission and cloud distribution morphologies. The observed emission from near- to mid-infrared wavelengths generally does not trace the bulk of the cloud distribution. The elongation of the emission is sensitive to the torus opening angle or scale height. For cloud distributions with a flat radial profile, polar extended emission is realized only at wavelengths shorter than ∼18 µm, and shorter than ∼5 µm for steep profiles. We make the full results available through Hypercat, a large hypercube of resolved AGN torus brightness maps computed with Clumpy. Hypercat also comprises software to process and analyze such large data cubes and provides tools to simulate observations with various current and future telescopes.

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