Cookies

We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.


Durham Research Online
You are in:

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

Ezhikode, Savithri H. and Gandhi, Poshak and Done, Chris and Ward, Martin and Dewangan, Gulab C. and 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). pp. 3492-3511.

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.

Item Type:Article
Full text:(VoR) Version of Record
Download PDF
(6026Kb)
Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/mnras/stx2160
Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:19 August 2017
Date deposited:01 November 2017
Date of first online publication:23 August 2017
Date first made open access:01 November 2017

Save or Share this output

Export:
Export
Look up in GoogleScholar