UV spectral diagnostics for low redshift quasars: estimating physical   conditions and radius of the Broad Line Region
  The UV spectral range (1100 - 3000 A) contains the strongest resonance lines observed in active galactic nuclei (AGN). Analysis of UV line intensity ratios and profile shapes in quasar spectra provide diagnostics of physical and dynamical conditions in the broad line emitting region. This paper discusses properties of UV lines in type-1 AGN spectra, and how they lead an estimate of ionizing photon flux, chemical abundances, radius of the broad line emitting region and central black hole mass. These estimates are meaningfully contextualised through the 4D "eigenvector-1" (4DE1) formalism. 
P. Marziani, J. W. Sulentic, C. A. Negrete, D. Dultzin, A. Del Olmo,   M. A. Mart\'inez Carballo, T. Zwitter, R. Bachev
astro-ph.GA