Estimating black hole masses in quasars using broad optical and UV emission lines

We review past work using broad emission lines as virial estimators of black hole masses in quasars. Basically one requires estimates of the emitting region radius and virial velocity dispersion to obtain black hole masses. The three major ways to estimate the broad-line emitting region (BLR) radius involve: (1) direct reverberation mapping, (2) derivation of BLR radius for larger samples using the radius-luminosity correlation derived from reverberation measures, and (3) estimates of BLR radius using the definition of the ionization parameter solved for BLR radius (photoionization method). At low redshift (z less than or similar to 0.7) FWHM H beta serves as the most widely used estimator of virial velocity dispersion. FWHM H beta can provide estimates for tens of thousands of quasars out to z approximate to 3.8 (IR spectroscopy beyond z approximate to 1). A new photoionization method also shows promise for providing many reasonable estimates of BLR radius via high S/N IR spectroscopy of the UV region 1300-2000 angstrom. FWHM Mgn lambda 22800 can serve as a surrogate for FWHM H beta in the range 0.4 8 z less than or similar to 6.5 while civ lambda 1549 is affected by broadening due to non-virial motions and best avoided (i.e. there is no clear conversion factor between FWHM H beta and FWHM Civ lambda 1549). Most quasars yield mass estimates in the range 7 less than or similar to log M-BH less than or similar to 9.7. There is no strong evidence for values above 10.0 and there may be evidence for a turnover in the maximum black hole mass near z approximate to 5. (C) 2011 Elsevier B.V. All rights reserved.