Quasars at z>~1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, CIV{lambda}1549, shows blueshifts up to ~5000km/s and in rare cases even higher. This blueshifting results in highly uncertain redshifts when compared to redshift determinations from rest-frame optical emission lines, e.g., from the narrow [OIII]{lambda}5007 feature. We present spectroscopic measurements for 260 sources at 1.55<~z<~3.50 having -28.0<~M_i_<~-30.0mag from the Gemini Near Infrared Spectrograph-Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the previous iteration, which contained 226 of the 260 sources whose measurements are improved upon in this work. We obtain reliable systemic redshifts based on [OIII]{lambda}5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a regression analysis involving CIV full-width-at-half-maximum intensity and equivalent width, along with the UV continuum luminosity at a rest-frame wavelength of 1350{AA}. Applying these corrections can improve the accuracy and the precision in the CIV-based redshift by up to ~850km/s and ~150km/s, respectively, which correspond to ~8.5 and ~1.5Mpc in comoving distance at z=2.5. Our prescriptions also improve the accuracy of the best available multifeature redshift determination algorithm by ~100km/s, indicating that the spectroscopic properties of the CIV emission line can provide robust redshift estimates for high-redshift quasars. We discuss the prospects of our prescriptions for cosmological and quasar studies utilizing upcoming large spectroscopic surveys.

Cone search capability for table J/ApJ/950/95/table1 (The Gemini Near Infrared Spectrograph--Distant Quasar Survey (GNIRS-DQS) observation log)