VLT/ISAAC Spectra of the H-beta Region in Intermediate-Redshift Quasars II. Black Hole Mass and Eddington Ratio

TL;DR

This study measures black hole masses and Eddington ratios in about 300 intermediate-redshift quasars using improved virial methods, revealing a realistic mass range and no significant super-Eddington accretion.

Contribution

It introduces a corrected FWHM measure for H-beta and compares it with FeII measures, enhancing accuracy in black hole mass estimates in AGNs.

Findings

Black hole masses range from 10^6 to 10^10 solar masses.

Corrected FWHM measures reduce overestimation of high masses.

No strong evidence for super-Eddington accretion in the sample.

Abstract

We derive black hole masses for a sample of about 300 AGNs in the redshift range 0 < z < 2.5. We use the same virial velocity measure (FWHM Hbeta broad component) 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 measure for the broad component of H-beta that better estimates the virialized line emitting component by comparing our FWHM measures with a sample of reverberated sources with H-beta radial velocity dispersion measures. We also consider the FWHM of the FeII 4570 blend as a potential alternative velocity estimator. We find a range of black hole mass between log M ~ 6 - 10, where the black hole mass M is in solar masses. Estimates using corrected FWHM, as well as FWHM(Fe II) measures, reduce the number of sources with log M > 9.5 and suggest that extremely large M values (log M >~ 10) may not be realistic. Derived Eddington ratio values 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(Hbeta broad component) <~ 4000 km/s show systematically higher Eddington ratio and lower M values than broader lined AGNs (including almost all radio-loud sources).