SDSS QSOs Al III and C III] emission lines

A. For Pop. xA, a small median blueshift of -250km/s was observed, motiva- ting a decomposition of the AlIII line profile into a virialized component centred at rest frame and a blueshifted component for an outflow emission. For Pop. B objects, we proved the empirical necessity to fit a redshifted very broad component (VBC), clearly seen in CIII], and analysed the physical implications on a Pop.

B composite spectrum using CLOUDY simulations. We find consistent black hole mass estimations using AlIII and CIII] as virial estimators for the bulk of Population A. AlIII (and even CIII]) is a reliable virial black hole mass estimator for Pop. A and B objects. xA sources deserve special attention due to the significant blueshifted excess observed in the line profile of AlIII, although not as large as those observed in CIV 1549.