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The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kα line emission in type 1 AGNs

The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kα line emission in type 1 AGNs
The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kα line emission in type 1 AGNs
The Fe Kα emission line is the most ubiquitous feature in the X-ray spectra of active galactic nuclei (AGNs), but the origin of its narrow core remains uncertain. Here, we investigate the connection between the sizes of the Fe Kα core emission regions and the measured sizes of the dusty tori in 13 local Type 1 AGNs. The observed Fe Kα emission radii (RFe) are determined from spectrally resolved line widths in X-ray grating spectra, and the dust sublimation radii (Rdust) are measured either from optical/near-infrared (NIR) reverberation time lags or from resolved NIR interferometric data. This direct comparison shows, on an object-by-object basis, that the dust sublimation radius forms an outer envelope to the bulk of the Fe Kα emission. RFe matches Rdust well in the AGNs, with the best constrained line widths currently. In a significant fraction of objects without a clear narrow line core, RFe is similar to, or smaller than, the radius of the optical broad line region. These facts place important constraints on the torus geometries for our sample. Extended tori in which the solid angle of fluorescing gas peaks at well beyond the dust sublimation radius can be ruled out. We also test for luminosity scalings of RFe, finding that the Eddington ratio is not a prime driver in determining the line location in our sample. We also discuss in detail potential caveats of data analysis and instrumental limitations, simplistic line modeling, uncertain black hole masses, and sample selection, showing that none of these is likely to bias our core result. The calorimeter on board Astro-H will soon vastly increase the parameter space over which line measurements can be made, overcoming many of these limitations.
galaxies, active, infrared, X-rays
1538-4357
1-11
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Hoenig, Sebastian F.
be0bb8bc-bdac-4442-8edc-f735834f3917
Kishimoto, Makoto
ffd0231d-af4a-467e-b693-82905e0ca7f3
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Hoenig, Sebastian F.
be0bb8bc-bdac-4442-8edc-f735834f3917
Kishimoto, Makoto
ffd0231d-af4a-467e-b693-82905e0ca7f3

Gandhi, Poshak, Hoenig, Sebastian F. and Kishimoto, Makoto (2015) The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kα line emission in type 1 AGNs. The Astrophysical Journal, 812 (113), 1-11. (doi:10.1088/0004-637X/812/2/113).

Record type: Article

Abstract

The Fe Kα emission line is the most ubiquitous feature in the X-ray spectra of active galactic nuclei (AGNs), but the origin of its narrow core remains uncertain. Here, we investigate the connection between the sizes of the Fe Kα core emission regions and the measured sizes of the dusty tori in 13 local Type 1 AGNs. The observed Fe Kα emission radii (RFe) are determined from spectrally resolved line widths in X-ray grating spectra, and the dust sublimation radii (Rdust) are measured either from optical/near-infrared (NIR) reverberation time lags or from resolved NIR interferometric data. This direct comparison shows, on an object-by-object basis, that the dust sublimation radius forms an outer envelope to the bulk of the Fe Kα emission. RFe matches Rdust well in the AGNs, with the best constrained line widths currently. In a significant fraction of objects without a clear narrow line core, RFe is similar to, or smaller than, the radius of the optical broad line region. These facts place important constraints on the torus geometries for our sample. Extended tori in which the solid angle of fluorescing gas peaks at well beyond the dust sublimation radius can be ruled out. We also test for luminosity scalings of RFe, finding that the Eddington ratio is not a prime driver in determining the line location in our sample. We also discuss in detail potential caveats of data analysis and instrumental limitations, simplistic line modeling, uncertain black hole masses, and sample selection, showing that none of these is likely to bias our core result. The calorimeter on board Astro-H will soon vastly increase the parameter space over which line measurements can be made, overcoming many of these limitations.

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arXiv:1502.02661 - Accepted Manuscript
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Accepted/In Press date: 31 August 2015
Published date: 14 October 2015
Keywords: galaxies, active, infrared, X-rays
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 400043
URI: http://eprints.soton.ac.uk/id/eprint/400043
ISSN: 1538-4357
PURE UUID: 97a4603b-6dda-4fd5-9d23-a254e866e9fb
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 08 Sep 2016 10:22
Last modified: 10 Dec 2019 01:33

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Contributors

Author: Poshak Gandhi ORCID iD
Author: Makoto Kishimoto

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