Measuring the level of nuclear activity in Seyfert galaxies and the unification scheme

¹ Indian Institute of Astrophysics, Bangalore 560034, India
e-mail: veeresh@iiap.res.in
² Department of Physics, University of Calicut, Calicut 673635, India
³ INAF-Osservatorio di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138, USA

Received: 6 June 2011
Accepted: 8 August 2011

Abstract

Context. The unification scheme of Seyfert galaxies hypothesizes that Seyfert type 1s and type 2s are intrinsically similar and the observed differences between the two subtypes are solely due to the differing orientations of toroidal-shaped obscuring material around the AGN. In the framework of the unification scheme, both the Seyfert subtypes are expected to show similar intrinsic nuclear properties such as the absorption-corrected AGN X-ray luminosity, bolometric luminosity, accretion rate and the mass of the supermassive black hole.

Aims. To test the predictions of the Seyfert unification scheme, we make statistical comparison of the distributions of: (i) the absorption-corrected 2.0–10 keV X-ray luminosities; (ii) the bolometric luminosities; (iii) the black hole masses and; (iv) the Eddington ratios, of Seyfert type 1s and type 2s.

Methods. We use an optically selected Seyfert sample in which type 1s and type 2s are matched in properties that are independent to the orientation of the obscuring torus, the AGN axis and the host galaxy.

Results. The distributions of the absorption-corrected 2.0–10 keV X-ray luminosities (${\mathit{L}}_{\mathrm{2.0}\mathrm{-}\mathrm{10} \mathrm{keV}}^{\mathrm{c}}$), the bolometric luminosities (L_Bol), the black masses (M_BH) and, the Eddington ratios (λ) are statistically similar for the two Seyfert subtypes, consistent with the orientation and obscuration based Seyfert unification scheme. The Eddington ratio distributions suggest that both the Seyfert subtypes are accreting at sub-Eddington level with wide span of Eddington ratios i.e.,10^-4–10^-1.