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The inter-line comparison between high- and low-ionization emission lines hasyielded a wealth of information on the quasar broad line region (BLR) structureand dynamics, including perhaps the earliest unambiguous evidence in favor of adisk + wind structure in radio-quiet quasars. We carried out an analysis of theCIV 1549 and Hbeta line profiles of 28 Hamburg-ESO high luminosity quasars andof 48 low-z, low luminosity sources in order to test whether thehigh-ionization line CIV 1549 width could be correlated with Hbeta and be usedas a virial broadening estimator. We analyze intermediate- to high-S/N,moderate resolution optical and NIR spectra covering the redshifted CIV andH$\beta$ over a broad range of luminosity log L ~ 44 - 48.5 [erg/s] andredshift (0 - 3), following an approach based on the quasar main sequence. Thepresent analysis indicates that the line width of CIV 1549 is not immediatelyoffering a virial broadening estimator equivalent to H$\beta$. At the same timea virialized part of the BLR appears to be preserved even at the highestluminosities. We suggest a correction to FWHM(CIV) for Eddington ratio (usingthe CIV blueshift as a proxy) and luminosity effects that can be applied overmore than four dex in luminosity. Great care should be used in estimatinghigh-L black hole masses from CIV 1549 line width. However, once correctedFWHM(CIV) values are used, a CIV-based scaling law can yield unbiased MBHvalues with respect to the ones based on H$\beta$ with sample standarddeviation ~ 0.3 dex.

Black hole mass estimates in quasars - A comparative analysis of high- and low-ionization lines