The diverse properties of broad-line quasars appear to follow a well-defined
main sequence along which the optical FeII strength increases. It has been
suggested that this sequence is mainly driven by the Eddington ratio (L/L_Edd)
of the black hole (BH) accretion. Shen & Ho demonstrated with quasar clustering
analysis that the average BH mass decreases with increasing FeII strength when
quasar luminosity is fixed, consistent with this suggestion. Here we perform an
independent test by measuring the stellar velocity dispersion sigma* (hence the
BH mass via the M-sigma* relation) from decomposed host spectra in low-redshift
Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity,
sigma* systematically decreases with increasing FeII strength, confirming that
Eddington ratio increases with FeII strength. We also found that at fixed
luminosity and FeII strength, there is little dependence of sigma* on the broad
Hbeta FWHM. These new results reinforce the framework put forward by Shen & Ho
that Eddington ratio and orientation govern most of the diversity seen in
broad-line quasar properties.Comment: ApJL in press; 5 pages and 4 figure
