Reverberation Measurements for 17 Quasars and the Size‐Mass‐Luminosity Relations in Active Galactic Nuclei

(abridged) We have spectrophotometrically monitored a well-defined sample of28 Palomar-Green quasars in order to obtain measurements of their BLRs and toinvestigate the relationships between quasar luminosity, central black holemass, and broad emission line region (BLR) size in active galactic nuclei(AGN). Spectrophotometry was obtained every 1-4 months for 7.5 years, yielding20-70 observing epochs per object. Both the continuum and emission line fluxesof all of the quasars were observed to change during the duration of theobserving program. Seventeen of the 28 objects were observed with adequatesampling to search for correlated variations between the Balmer emission linesand the continuum flux. For each of these 17 objects, a significant correlationwas observed, with the Balmer line variations lagging those of the continuum by\~100 days (rest frame). Our work increases the available luminosity range forstudying the size-mass-luminosity relations in AGN by two orders of magnitudeand doubles the number of objects suitable for such studies. Combining ourresults with comparable published data available for Seyfert 1 galaxies, wefind the BLR size scales with the rest-frame 5100 A luminosity asL^{0.70+-0.03}. This determination of the scaling of the size of the BLR as afunction of luminosity is significantly different from those previouslypublished, and suggests that the effective ionization parameter in AGN may be adecreasing function of luminosity. We are also able to constrain, subject toour assumption that gravity dominates the motions of the BLR gas, the scalingrelationship between the mass of the central black holes and the luminosity inAGN: M \propto L^{0.5+-0.1}. This is inconsistent with all AGN having opticalluminosity that is a constant fraction of the Eddington luminosity.Comment: 21 pages, 8 figures included, LaTeX emulateapj.sty, accepted for publication in the Astrophysical Journal. Resubmitting to Correct few confusing sentences in subsection 5.