Reverberation Measurements of Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei

Abstract

A 7.5 years spectrophotometric monitoring program of 28 Palomar-Green quasars to determine the size of their broad emission line region (BLR) is reviewed. We find both the continuum and the emission line fluxes of all quasars to vary during this period. Seventeen objects has adequate sampling for reverberation mapping and in all of them we find the Balmer line variations to lag those of the continuum by ~100 days. This study increases the available luminosity range for studying the size-mass-luminosity relations in active galactic nuclei (AGNs) by two orders of magnitude and doubles the number of objects suitable for such studies. Combining our results with data available for Seyfert 1 galaxies, we find the BLR size to scale with the rest-frame 5100 A luminosity as L^{0.70 +/- 0.03}. This result is different from previous studies, and suggests that the effective ionization parameter in AGNs may be a decreasing function of luminosity. We are also able to constrain, subject to the assumption that gravity dominates the motions of the BLR gas, the scaling relation between the mass of the central black hole and the AGN's luminosity. We find that the central mass scales with the 5100 A luminosity as M\proptoL^{0.5 +/- 0.1}. A program to monitor 11 high-luminosity quasars is presented here for the first time. Preliminary results from this program indicate continuum variation of order of 0.1 mag in all objects. We illustrate the importance and feasibility of monitoring those objects spectrophotometrically. When this program will be completed reverberation mapping studies will cover the entire AGNs luminosity range from 10^{41} to 10^{48} ergs/s.