Revisiting the Hβ Size–Luminosity Relation Using a Uniform Reverberation-mapping Analysis

Abstract

We revisit the relation between active galactic nucleus (AGN) broad-line region (BLR) size and luminosity by conducting a uniform Hβ reverberation-mapping analysis for 212 AGNs with archival light curves. Our analysis incorporates three different lag measurement methods, including the interpolated cross-correlation function (ICCF), JAVELIN, and PyROA, alongside a consistently defined lag-searching window and an alias removal procedure. We find that ICCF, albeit with larger uncertainties compared to other methods, is the most reliable method based on our visual inspection of the matches between Hβ and the shifted continuum light curves. Combining this sample with the 32 AGNs from Seoul National University AGN Monitoring Project, we obtain the best-fit relation between the BLR size (R BLR) and the continuum luminosity at 5100 Å (L 5100) with a slope significantly flatter than 0.5. By selecting a subsample of 157 AGNs with the best-quality lag measurements using a set of quantitative criteria and visual inspection, we find a consistent slope and a slightly decreased intrinsic scatter. We further investigate the effect of luminosity tracers, including L 5100, Hβ luminosity (L Hβ ), [O iii] luminosity (L [O III]), and 2–10 keV hard X-ray luminosity L 2–10keV. We find that sub-Eddington and super-Eddington AGNs exhibit systematic offsets in both R BLR–L 5100 and R BLR–L Hβ relations, while they show comparable R BLR–L [O III] and R BLR–L 2–10keV relations. We discuss the potential causes for these different deviations when employing different luminosity tracers.