Quasar emission lines as virial luminosity estimators

PM and MDO acknowledge funding from the INAF PRINSKA 2017 program 1.05.01.88.04. PM is also gtrateful for support via a STSM of the COST Action CA16104, Gravitational waves, black holes and fundamental physics that allowed her participation to the SCSLSA12. AdO acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through grant AYA2016-76682-C3-1-P and from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award for the Instituto de Astrof ' isica de Andaluc ' ia (SEV-2017-0709). E.B. and N.B. acknowledge support from the Ministry of Education, Science and Technological Development of the Republic of Serbia through the projects Astrophysical Spectroscopy of Extragalactic Objects (176001) and Gravitation and structure of the Universe on large scales (176003).