Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGN: The Effects of Cloud Orientation and Anisotropic Illumination

Abstract

The obscuring circumnuclear torus of dusty molecular gas is one of the major components of active galactic nuclei (AGN). The torus can be studied by analyzing the time response of its infrared (IR) dust emission to variations in the AGN continuum luminosity, a technique known as reverberation mapping. The IR response is the convolution of the AGN ultraviolet/optical light curve with a transfer function that contains information about the size, geometry, and structure of the torus. Here, we describe a new computer model that simulates the reverberation response of a clumpy torus. Given an input optical light curve, the code computes the emission of a 3D ensemble of dust clouds as a function of time at selected IR wavelengths, taking into account light travel delays. We present simulated dust emission responses at 3.6, 4.5, and 30 $\mu$m that explore the effects of various geometrical and structural properties, dust cloud orientation, and anisotropy of the illuminating radiation field. We also briefly explore the effects of cloud shadowing (clouds are shielded from the AGN continuum source). Example synthetic light curves have also been generated, using the observed optical light curve of the Seyfert 1 galaxy NGC 6418 as the input. The torus response is strongly wavelength-dependent, due to the gradient in cloud surface temperature within the torus, and because the cloud emission is strongly anisotropic at shorter wavelengths. Anisotropic illumination of the torus also significantly modifies the torus response, reducing the lag between the IR and optical variations.

17 pages, 14 figures, published in the Astrophysical Journal (2017 July 1)

References in corpus (14)

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• Radiative Transfer Modeling of Three-Dimensional Clumpy AGN Tori and its Application to NGC 1068
• Reverberation Measurements of the Inner Radius of the Dust Torus in 17 Seyfert Galaxies
• The innermost region of AGN tori: implications from the HST/NICMOS Type 1 point sources and near-IR reverberation
• Three-dimensional radiative transfer models of clumpy tori in Seyfert galaxies
• Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured
• Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: Revealing the inner funnel of dust
• The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus models
• 9.7 um Silicate Features in AGNs: New Insights into Unification Models
• High-Velocity Bipolar Molecular Emission from an AGN Torus
• Nuclear 11.3$\mu$m PAH emission in local active galactic nuclei
• Gemini Mid-IR Polarimetry of NGC1068: Polarized Structures Around the Nucleus
• Spitzer Space Telescope Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418

Cited by in corpus (16)

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• Torus and polar dust dependence on AGN properties
• The rise and fall of the iron-strong nuclear transient PS16dtm
• The Dusty Heart of NGC 4151 Revealed by $\lambda \sim$1-40 $\mu$m Reverberation Mapping and Variability: A Challenge to Current Clumpy Torus Models
• Multiphase Gas Nature in the Sub-parsec Region of the Active Galactic Nuclei I: Dynamical Structures of Dusty and Dust-free Outflow
• Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGNs: An Investigation of Torus Response Functions
• The role of grain size in AGN torus dust models
• Dust Reverberation Mapping of Z229-15
• A Mid-infrared Flare in the Active Galaxy MCG-02-04-026: Dust Echo of a Nuclear Transient Event
• The 'Big Dipper': The nature of the extreme variability of the AGN SDSS J2232-0806
• The Study of Circumgalactic Medium with Quasar Pairs
• The Relative Wavelength Independence of IR Time Lags in NGC4151 During the Years 2010-2015
• Dust Reverberation Mapping and Light-Curve Modelling of Zw229-015
• Detection of eccentric close-binary supermassive black holes with incomplete interferometric data
• Modeling the Reverberation Response of the Broad Line Region in Active Galactic Nuclei II: Incorporating Photoionization Models