0 Assigned ID: 1414 ----- Attempting Submission 1 (Fri Mar 01 06:46:54 GMT 2013) ----- Single-epoch ultraviolet spectra of quasars may be used to estimate the mass of central supermassive black hole, especially at high redshifts when this region is more conveniently observed in the optical. Virial motion is assumed, and the continuum is used to estimate the line emitting size scale, while the broad C IV profile is used to estimate the velocity of the gas. HST data have been used to calibrate such a C IV scaling relationship, which has significant scatter and has been criticized on several fronts. We have developed an approach to significantly reduce the uncertainty of C IV based masses that rests on a better understanding of a major source of scatter, and have also identified a significant bias in previously published C IV scaling relationships, such that masses are about 50 percent too small on average. Using a combination of HST and ground-based data, we propose to further develop and publish both an average correction to C IV-based masses as well as a new correction term, based on easy and robust spectral measurements, resulting in greatly improved masses. We will also produce a mass estimator based on Lyman alpha, convenient for the highest redshift quasars. Finally, we will test the new formulations against high-redshift, high-luminosity quasars with Lyman alpha, C IV, and Hbeta spectra available, using consistent measurement techniques and make luminosity dependent corrections as needed. As a byproduct, we will produce a catalog of consistent measurements of HST-observed UV quasar spectra along with ground-based optical spectra. AGN/QUASARS Default Small false true false false false SUPPORTED