The most reliable single-epoch supermassive black hole mass (MBH) estimates in quasars are obtained by using the velocity widths of low-ionization emission lines, typically the H{beta}{lambda}4861 line. Unfortunately, this line is redshifted out of the optical band at z~1, leaving MBH estimates to rely on proxy rest-frame ultraviolet (UV) emission lines, such as CIV{lambda}1549 or MgII{lambda}2800, which contain intrinsic challenges when measuring, resulting in uncertain MBH estimates. In this work, we aim at correcting MBH estimates derived from the CIV and MgII emission lines based on estimates derived from the H{beta} emission line. We find that employing the equivalent width of CIV in deriving MBH estimates based on MgII and CIV provides values that are closest to those obtained from H{beta}. We also provide prescriptions to estimate MBH values when only CIV, only MgII, and both CIV and MgII are measurable. We find that utilizing both emission lines, where available, reduces the scatter of UV-based MBH estimates by ~15% when compared to previous studies. Lastly, we discuss the potential of our prescriptions to provide more accurate and precise estimates of MBH given a much larger sample of quasars at 3.20R<~z<~3.50, where both MgII and H{beta} can be measured in the same near-infrared spectrum.

Cone search capability for table J/ApJ/950/96/table1 (CIV and MgII spectroscopic measurements)

Cone search capability for table J/ApJ/950/96/table3 (M_BH_ estimates)