MARZIANI, PaolaPaolaMARZIANIBon, EdiEdiBonBon, NatasaNatasaBondel Olmo, AscensionAscensiondel OlmoMartínez-Aldama, MaryMaryMartínez-AldamaD'ONOFRIO, MAUROMAUROD'ONOFRIODultzin, DeborahDeborahDultzinNegrete, C.C.NegreteSTIRPE, Giovanna MariaGiovanna MariaSTIRPE2021-01-292021-01-2920192218-2004http://hdl.handle.net/20.500.12386/30096Quasars accreting matter at very high rates (known as extreme Population A [xA] or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars radiate at a stable, extreme luminosity-to-mass ratio. This in turns translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the main optical and UV spectral properties of extreme Population A quasars that make them easily identifiable in large spectroscopic surveys at low-z (z < 1) and intermediate-z (2 < z < 2.6), and the physical conditions that are derived for the formation of their emission lines. Ultimately, the analysis supports the possibility of identifying a virial broadening estimator from low-ionization line widths, and the conceptual validity of the redshift-independent luminosity estimates based on virial broadening for a known luminosity-to-mass ratio.STAMPAenArticle10.3390/atoms70100182-s2.0-85066464116000464279000001https://www.mdpi.com/2218-2004/7/1/18https://arxiv.org/abs/1901.100322019Atoms...7...18MFIS/05 - ASTRONOMIA E ASTROFISICA