Central Masses and Broad‐Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation‐Mapping Database

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