On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies

¹ Instituto de Física de Cantabria (CSIC-UC), Avda. de los Castros, 39005 Santander, Spain e-mail: panessa@ifca.unican.es
² INAF – IASF, via P. Gobetti 101, 40129 Bologna, Italy
³ The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St. Pasadena, CA 91101, USA
⁴ Max Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany

Received: 23 January 2006
Accepted: 4 May 2006

Abstract

We investigate the relation between X-ray nuclear emission, optical emission line luminosities and black hole masses for a sample of 47 Seyfert galaxies. The sample, which has been selected from the Palomar optical spectroscopic survey of nearby galaxies (Ho et al. 1997a, ApJS, 112, 315), covers a wide range of nuclear powers, from ~ 10⁴³ erg/s down to very low luminosities ( ~ 10³⁸ erg/s). Best available data from Chandra, XMM-Newton and, in a few cases, ASCA observations have been considered. Thanks to the good spatial resolution available from these observations and a proper modeling of the various spectral components, it has been possible to obtain accurate nuclear X-ray luminosities not contaminated by off-nuclear sources and/or diffuse emission. X-ray luminosities have then been corrected taking into account the likely candidate Compton thick sources, which are a high fraction (>30%) among type 2 Seyferts in our sample. The main result of this study is that we confirm strong linear correlations between 2–10 keV, [OIII]λ5007, H_α luminosities which show the same slope as quasars and luminous Seyfert galaxies, independent of the level of nuclear activity displayed. Moreover, despite the wide range of Eddington ratios () tested here (six orders of magnitude, from 0.1 down to ~10^-7), no correlation is found between the X-ray or optical emission line luminosities and the black hole mass. Our results suggest that Seyfert nuclei in our sample are consistent with being a scaled-down version of more luminous AGN.