VLT/ISAAC spectra of the Hβ region in intermediate-redshift quasars

II. Black hole mass and Eddington ratio

¹ Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA e-mail: giacomo@merlot.astr.ua.edu
² Osservatorio Astronomico di Padova, INAF, Vicolo dell' Osservatorio 5, 35122 Padova, Italy e-mail: [marziani;calvani]@pd.astro.it
³ Instituto de Astronomía, UNAM, Aptdo. Postal 70-264, México, D. F. 04510, México e-mail: [prepetto;deborah]@astroscu.unam.mx
⁴ Osservatorio Astronomico di Bologna, INAF, via Ranzani 1, 40127 Bologna, Italy e-mail: stirpe@bo.astro.it

Received: 5 September 2005
Accepted: 16 June 2006

Abstract

We derive black hole masses for a sample of about 300 AGNs in the redshift range . We use the same virial velocity measure (FWHM H) for all sources which represents a significant improvement over previous studies. We review methods and caveats for determining AGN black hole masses via the virial assumption for motions in the gas producing low ionization broad emission lines. We derive a corrected FWHM(H) measure for the broad component of Hβ that better estimates the virialized line emitting component by comparing our FWHM measures with a sample of reverberated sources with Hβ radial velocity dispersion measures. We also consider the FWHM of the Feiiλ 4570 blend as a potential alternative velocity estimator. We find a range of black hole mass between  M_BH ~ 6.0–10.0, where M_BH is in solar masses. Estimates using corrected FWHM(Hβ), as well as FWHM(Feii) measures, reduce the number of sources with M_BH > 9.5 and suggest that extremely large M_BH values ( M_BH  10) may not be realistic. Derived  values show no evidence for a significant population of super-Eddington radiators especially after correction is made for sources with extreme orientation to our line of sight. Sources with FWHM(H) 4000 km s^-1 show systematically higher  and lower M_BH values than broader lined AGNs (including almost all radio-loud sources).