The Intermediate-ionization Lines as Virial Broadening Estimators for Population A Quasars*

The identification of a virial broadening estimator in the quasar UV rest frame suitable for black hole mass computation at high redshift has become an important issue. We compare HI Balmer H-beta line width to ones two intermediate ionization lines: Aliii 1860 doublet and Ciii] 1909 line, over wide interval luminosity (0 < z 3.5; 43 logL 48.5 [erg a/]), 48 sources belonging population characterized by mid-to-high values Eddington ratio (Population A). present analysis indicates that are highly correlated, can be considered equivalent most Population A quasars five orders magnitude luminosity; forCiii] 1909, multiplication constant correction factor xi ~ 1.25 is sufficient bring FWHM agreement with one H-betaa. statistical concordance between low-ionization intermediate-ionization lines suggests they predominantly arise from same virialized part broad region. However, blueshifts modest amplitude (few hundred km /s) respect excess (~ 1.1) found fraction our sample. Scaling laws estimate M_BH using widths have rms scatter 0.3 dex. scaling law takes form log 0.58 L1700,44 + 2 0.49 [solar masses].