SIMBAD references

We present Mg II-based black hole (BH) mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad-line region (BLR) and the continuum luminosity at 3000 Å. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the Hubble Space Telescope/International Ultraviolet Explorer databases which have corresponding reverberation mapping estimates of the Hβ BLR's radius. Our mass estimation method uses the line dispersion rather than the full width at half-maximum of the low-ionization Mg II emission line. We measure Mg II line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in BH mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the BH masses to lower than 0.15 dex.