We present improved black hole masses for 35 active galactic nuclei (AGNs) based on a complete and consistent reanalysis of broad emission-line reverberation-mapping data. From objects with multiple line measurements, we find that the highest precision measure of the virial product cτ ∆V 2 /G, where τ is the emission-line lag relative to continuum variations and ∆V is the emission-line width, is obtained by using the crosscorrelation function centroid (as opposed to the cross-correlation function peak) for the time delay and the line dispersion (as opposed to full width half maximum) for the line width and by measuring the line width in the variable part of the spectrum. Accurate line-width measurement depends critically on avoiding contaminating features, in particular the narrow components of the emission lines. We find that the precision (or random component of the error) of reverberation-based black hole mass measurements is typically around 30%, comparable to the precision attained in measurement of black hole masses in quiescent galaxies by gas or stellar dynamical methods. Based on results

We calibrate reverberation-based black hole masses in active galactic nuclei (AGNs) by using the correlation between black hole mass, M BH , and bulge/spheroid stellar velocity dispersion, σ * . We use new measurements of σ * for 6 AGNs and published velocity dispersions for 10 others, in conjunction with improved reverberation mapping results, to determine the scaling factor required to bring reverberation-based black hole masses into agreement with the quiescent galaxy M BH -σ * relationship. The scatter in the AGN BH masses is found to be less than a factor of 3. The current observational uncertainties preclude use of the scaling factor to discriminate between broad-line region models.

The masses and emission-line region sizes of AGNs can be measured by "reverberation-mapping" techniques and we use these results to calibrate similar determinations made by photoionization models of the AGN line-emitting regions. Reverberation mapping uses the light travel-time delayed emission-line response to continuum variations to determine the size and kinematics of the emission-line region. We compile a sample of 17 Seyfert 1 galaxies and 2 quasars with reliable reverberation and spectroscopy data, twice the number available previously. The data provide strong evidence that the BLR size (as measured by the lag of the emission-line luminosity after changes in the continuum) and the emission-line width measure directly the central mass: the virial assumption is tested with long-term UV and optical monitoring data on NGC 5548. Two methods are used to estimate the distance of the broad emission-line region (BLR) from the ionizing source: the photoionization method (which is available for many AGNs but has large intrinsic uncertainties), and the reverberation method (which gives very reliable distances, but is available for only a few objects). The distance estimate is combined with the velocity dispersion, derived from the broad Hβ line width (in the photoionization method) or from the variable part (RMS) of the line profile, in the reverberation -RMS method, to estimate the virial mass. Comparing the central masses calculated with the reverberation -RMS method to those calculated using a photoionization model, we find a highly significant, nearly linear correlation. This provides a calibration of the photoionization method on the objects with presently available reverberation data, which should enable mass estimates for all AGNs with measured Hβ line width. We find that the correlation between the masses is significantly better than the correlation between the corresponding BLR sizes calculated by the two methods, which further supports the conclusion that both methods measure the mass of the central black hole. Comparing the BLR sizes given by the two methods also enables us to estimate the ionizing EUV luminosity L ion which is directly unobservable. Typically it is ten times the monochromatic luminosity at 5100Å(L v ). The Eddington ratio for the objects in our sample is in the range L v /L Edd ∼ 0.001 − 0.03 and L ion /L Edd ≈ 0.01 − 0.3.

We report the first results of a program to measure accurate stellar velocity dispersions in the bulges of the host galaxies of active galactic nuclei (AGNs) for which accurate black hole (BH) masses have been determined via reverberation mapping. We find good agreement between BH masses obtained from reverberation mapping, and from the M • − σ relation as defined by quiescent galaxies, indicating a common relationship between active and quiescent black holes and their larger-scale environments.