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Modeling the infrared reverberation response of the circumnuclear dusty torus in AGNs: An investigation of torus response functions

Modeling the infrared reverberation response of the circumnuclear dusty torus in AGNs: An investigation of torus response functions
Modeling the infrared reverberation response of the circumnuclear dusty torus in AGNs: An investigation of torus response functions
The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGNs) can be investigated by analyzing the temporal response of the torus's infrared (IR) dust emission to variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths (≤4.5 μm). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of ~3, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberation mapping. However, overall, the models predict radii at 2.2 μm that are typically a factor of ~2 larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.
0004-637X
Almeyda, Triana
4c79d019-6f06-46fc-803c-741a128c9c85
Robinson, Andrew
11e9f1f6-1445-436a-a482-7208201c83ac
Richmond, Michael
81e64abd-462a-4c54-be7c-ec83e8a27081
Nikutta, Robert
2146fc7a-e52c-438a-82bc-63cfcf16c587
McDonough, Bryanne
26cea562-64aa-4d10-abac-6ac06d7b8688
Almeyda, Triana
4c79d019-6f06-46fc-803c-741a128c9c85
Robinson, Andrew
11e9f1f6-1445-436a-a482-7208201c83ac
Richmond, Michael
81e64abd-462a-4c54-be7c-ec83e8a27081
Nikutta, Robert
2146fc7a-e52c-438a-82bc-63cfcf16c587
McDonough, Bryanne
26cea562-64aa-4d10-abac-6ac06d7b8688

Almeyda, Triana, Robinson, Andrew, Richmond, Michael, Nikutta, Robert and McDonough, Bryanne (2020) Modeling the infrared reverberation response of the circumnuclear dusty torus in AGNs: An investigation of torus response functions. The Astrophysical Journal, 891 (1), [26]. (doi:10.3847/1538-4357/ab6aa1).

Record type: Article

Abstract

The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGNs) can be investigated by analyzing the temporal response of the torus's infrared (IR) dust emission to variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths (≤4.5 μm). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of ~3, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberation mapping. However, overall, the models predict radii at 2.2 μm that are typically a factor of ~2 larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.

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Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGNs: An Investigation of Torus Response Functions - Accepted Manuscript
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Accepted/In Press date: 11 January 2020
e-pub ahead of print date: 28 February 2020
Published date: 1 March 2020

Identifiers

Local EPrints ID: 439483
URI: http://eprints.soton.ac.uk/id/eprint/439483
ISSN: 0004-637X
PURE UUID: 417c1a3a-2dc5-46ee-8b54-20bc5e1d3818

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Date deposited: 24 Apr 2020 16:30
Last modified: 27 Apr 2022 05:45

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Contributors

Author: Triana Almeyda
Author: Andrew Robinson
Author: Michael Richmond
Author: Robert Nikutta
Author: Bryanne McDonough

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