A new method to obtain the broad line region size of high redshift quasars

We present high signal-to-noise ratio UV spectra for eight quasars at z 3 obtained with Very Large Telescope/FORS. The spectra enable us to analyze in detail the strong and weak emission features in the rest frame range 1300-2000 Å of each source (C III] λ1909, Si III] λ1892, Al III λ1860, Si II λ1814, C IV λ1549 and blended Si IV λ1397+O IV] λ1402). The flux ratios Al III λ1860/Si III] λ1892, C IV λ1549/Al III λ1860, Si IV λ1397+O IV] λ1402/Si III] λ1892 and Si IV λ1397+O IV] λ1402/C IV λ1549 strongly constrain ionizing photon flux and metallicity through the use of diagnostic maps built from CLOUDY simulations. The radius of the broad line region is then derived from the ionizing photon flux applying the definition of the ionization parameter. The r BLRestimate and the width of a virial component isolated in prominent UV lines yields an estimate of black hole mass. We compare our results with previous estimates obtained from the r BLR-luminosity correlation customarily employed to estimate the black hole masses of high redshift quasars. © 2014. The American Astronomical Society. All rights reserved..