The Radius-Luminosity Relationship Depends on Optical Spectra in Active
  Galactic Nuclei
  The radius-luminosity (R-L) relationship of active galactic nuclei (AGNs)
established by the reverberation mapping (RM) observations has been widely used
as a single-epoch black hole mass estimator in the research of large AGN
samples. However, the recent RM campaigns discovered that the AGNs with high
accretion rates show shorter time lags by factors of a few comparing with the
predictions from the R-L relationship. The explanation of the shortened time
lags has not been finalized yet. We collect 8 different single-epoch spectral
properties to investigate how the shortening of the time lags correlate with
those properties and to understand what is the origin of the shortened lags. We
find that the flux ratio between Fe II and H$\beta$ emission lines shows the
most prominent correlation, thus confirm that accretion rate is the main driver
for the shortened lags. In addition, we establish a new scaling relation
including the relative strength of Fe II emission. This new scaling relation
can provide less biased estimates of the black hole mass and accretion rate
from the single-epoch spectra of AGNs.
