Notes. (1): QSO ID. (2) and (3): RA and Dec (J2000) from Bañados et al. (2016, 2018a). (4): Redshift and emission line from which it is derived. In cases of different values derived from different emission lines for the same source, we preferred the redshift derived from the [C II] line rather than the Mg II line, as discussed in Sect. 2.3. (5): Absolute and apparent magnitude at 1450 Å. M_{1450 Å} can vary by up to ≈0.3 mag among different papers, depending on the prescription used to compute it (e.g., Omont et al. 2013 vs. Bañados et al. 2016 for CFHQS J1641+3755). We consistently assumed the values reported by Bañados et al. (2016) and Mazzucchelli et al. (2017), which used the same prescription, for all our sources. (6): Bolometric luminosity estimated from M_{1450 Å}, using the bolometric correction of Venemans et al. (2016). (7): Virial black-hole mass estimated from the Mg II emission line. We note that Trakhtenbrot et al. (2017b) used different calibrations for the black-hole masses of several QSOs included in our sample, typically resulting in larger values (up to ≈0.2 − 0.3 dex). (8): Eddington ratio: λ_Edd = L_bol/L_Edd. (10): Radio-loudness parameter (see Sect. 2.3)

^( * )For these QSOs, black-hole masses have been modified according to the Vestergaard & Osmer (2009) calibration, to be consistent with the other QSOs. In these cases, the references indicate the papers from which FWHM(Mg II) and L_{3000 Å} are collected.

References. For the QSO discovery, adopted redshift, and black-hole mass. B15: Bañados et al. (2015a); B18a: Bañados et al. (2018a); C15: Carnall et al. (2015); dR11: De Rosa et al. (2011); D18: Decarli et al. (2018); F01: Fan et al. (2001); F03: Fan et al. (2003); F04: Fan et al. (2004); I04: Iwamuro et al. (2004); J08: Jiang et al. (2008); J16: Jiang et al. (2016); K07: Kurk et al. (2007); K09: Kurk et al. (2009); M11: Mortlock et al. (2011); M16: Matsuoka et al. (2016); M17: Mazzucchelli et al. (2017); V12: Venemans et al. (2012); V13: Venemans et al. (2013); V15: Venemans et al. (2015); V16: Venemans et al. (2016); V17: Venemans et al. (2017); W07: Willott et al. (2007); W09: Willott et al. (2009); W10: Willott et al. (2010); W13: Willott et al. (2013); Wa10: Wang et al. (2010); Wa11: Wang et al. (2011); Wa13: Wang et al. (2013); Wa16: Wang et al. (2016); Wu15: Wu et al. (2015).