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Determining the torus covering factors for a sample of type 1 AGN in the local Universe

Determining the torus covering factors for a sample of type 1 AGN in the local Universe
Determining the torus covering factors for a sample of type 1 AGN in the local Universe
In the unified scheme of active galactic nuclei, a dusty torus absorbs and then reprocesses a fraction of the intrinsic luminosity which is emitted at longer wavelengths. Thus, subject to radiative transfer corrections, the fraction of the sky covered by the torus as seen from the central source (known as the covering factor fc) can be estimated from the ratio of the infrared to the bolometric luminosities of the source as fc = Ltorus/LBol. However, the uncertainty in determining LBol has made the estimation of covering factors by this technique difficult, especially for AGN in the local Universe where the peak of the observed spectral energy distributions lies in the UV (ultraviolet). Here, we determine the covering factors of an X-ray/optically selected sample of 51 type 1 AGN. The bolometric luminosities of these sources are derived using a self-consistent, energy-conserving model that estimates the contribution in the unobservable far-UV region, using multifrequency data obtained from SDSS, XMM–Newton, WISE, 2MASS and UKIDSS. We derive a mean value of fc ∼ 0.30 with a dispersion of 0.17. Sample correlations, combined with simulations, show that fc is more strongly anticorrelated with λEdd than with LBol. This points to large-scale torus geometry changes associated with the Eddington-dependent accretion flow, rather than a receding torus, with its inner sublimation radius determined solely by heating from the central source. Furthermore, we do not see any significant change in the distribution of fc for sub-samples of radio-loud sources or Narrow Line Seyfert 1 galaxies (NLS1s), though these sub-samples are small.
0035-8711
3492-3511
Ezhikode, Savithri
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Gandhi, Poshak
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Done, Chris
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Ward, Martin
e15fea71-9056-429d-a4ba-f43a31583f42
Dewangan, Gulab C.
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Misra, Ranjeev
2285adb3-8a4c-47f7-b073-e5f36c7dd6ad
Philip, Ninan Sajeeth
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Ezhikode, Savithri
d64a5c12-d7a5-46eb-9546-771f8f5aecc8
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Done, Chris
f21f3c76-9341-4bc2-bbeb-d9a91c1ccee4
Ward, Martin
e15fea71-9056-429d-a4ba-f43a31583f42
Dewangan, Gulab C.
5ac9d24b-bcbb-45ab-a838-b093e67fc990
Misra, Ranjeev
2285adb3-8a4c-47f7-b073-e5f36c7dd6ad
Philip, Ninan Sajeeth
dac5e42b-e2e6-4587-bb10-f69fbdddebdf

Ezhikode, Savithri, Gandhi, Poshak, Done, Chris, Ward, Martin, Dewangan, Gulab C., Misra, Ranjeev and Philip, Ninan Sajeeth (2017) Determining the torus covering factors for a sample of type 1 AGN in the local Universe. Monthly Notices of the Royal Astronomical Society, 472 (3), 3492-3511. (doi:10.1093/mnras/stx2160).

Record type: Article

Abstract

In the unified scheme of active galactic nuclei, a dusty torus absorbs and then reprocesses a fraction of the intrinsic luminosity which is emitted at longer wavelengths. Thus, subject to radiative transfer corrections, the fraction of the sky covered by the torus as seen from the central source (known as the covering factor fc) can be estimated from the ratio of the infrared to the bolometric luminosities of the source as fc = Ltorus/LBol. However, the uncertainty in determining LBol has made the estimation of covering factors by this technique difficult, especially for AGN in the local Universe where the peak of the observed spectral energy distributions lies in the UV (ultraviolet). Here, we determine the covering factors of an X-ray/optically selected sample of 51 type 1 AGN. The bolometric luminosities of these sources are derived using a self-consistent, energy-conserving model that estimates the contribution in the unobservable far-UV region, using multifrequency data obtained from SDSS, XMM–Newton, WISE, 2MASS and UKIDSS. We derive a mean value of fc ∼ 0.30 with a dispersion of 0.17. Sample correlations, combined with simulations, show that fc is more strongly anticorrelated with λEdd than with LBol. This points to large-scale torus geometry changes associated with the Eddington-dependent accretion flow, rather than a receding torus, with its inner sublimation radius determined solely by heating from the central source. Furthermore, we do not see any significant change in the distribution of fc for sub-samples of radio-loud sources or Narrow Line Seyfert 1 galaxies (NLS1s), though these sub-samples are small.

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Accepted/In Press date: 19 August 2017
e-pub ahead of print date: 23 August 2017
Published date: 11 December 2017
Additional Information: Author Gandhi confirmed 1610.00429v2 is AM copy.

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Local EPrints ID: 416289
URI: http://eprints.soton.ac.uk/id/eprint/416289
ISSN: 0035-8711
PURE UUID: f33eee60-b719-4cd4-aa51-330cdcc0cafd
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 11 Dec 2017 17:30
Last modified: 07 Oct 2020 02:06

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Author: Savithri Ezhikode
Author: Poshak Gandhi ORCID iD
Author: Chris Done
Author: Martin Ward
Author: Gulab C. Dewangan
Author: Ranjeev Misra
Author: Ninan Sajeeth Philip

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