Placing High-redshift Quasars in Perspective: A Catalog of Spectroscopic Properties from the Gemini Near Infrared Spectrograph–Distant Quasar Survey

Abstract

We present spectroscopic measurements for 226 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample (m i ≲ 19.0 mag, H ≲ 16.5 mag) of Sloan Digital Sky Survey (SDSS) quasars at 1.5 ≲ z ≲ 3.5 with a monochromatic luminosity ( ) at 5100 Å in the range of 1044–1046 erg s−1. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C iv λ1549, Mg ii λλ2798, 2803, Hβ λ4861, and [O iii] λλ4959, 5007 emission lines, in each source. The spectral inventory will be utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements will facilitate an understanding of the dependence of rest-frame ultraviolet–optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time.

Can X-Ray Observations Improve Optical-UV-based Accretion-rate Estimates for Quasars?

“…A larger sample size of preferentially high-luminosity, highredshift sources (whereby UV data can be obtained from optical spectra, e.g., from SDSS) is needed for testing the correlations presented in this work in an unbiased way and drawing firmer conclusions. Because luminous sources that have high-quality archival X-ray, C IV, and Hβ measurements are rare, we plan to obtain X-ray snapshot observations of sources from the largest uniform compilation of high-redshift quasars with Hβ measurements (Matthews et al 2021), thus more than doubling the current inventory. In future investigations, we plan to measure the C IV blueshift (using the [O III]based systemic redshift) and compute the C IV "distance" as proposed by Rivera et al (2020) to replace the use of the C IV EW and blueshift separately.…”

Can X-ray Observations Improve Optical-UV-based Accretion-Rate Estimates for Quasars?

“…A larger sample size of preferentially high-luminosity, high-redshift sources (whereby UV data can be obtained from optical spectra, e.g., from SDSS) is needed for testing the correlations presented in this work in an unbiased way and drawing firmer conclusions. Since luminous sources that have high-quality archival X-ray, C IV, and Hβ measurements are rare, we plan to obtain X-ray snapshot observations of sources from the largest, uniform compilation of high-redshift quasars with Hβ measurements (Matthews et al 2021), thus more than doubling the current inventory. In future investigations, we plan to measure the C IV blueshift (using the [O III]-based systemic redshift) and compute the C IV "distance" as proposed by Rivera et al (2020), to replace the use of the C IV EW and blueshift separately.…”

Systematically smaller single-epoch quasar black hole masses using a radius-luminosity relationship corrected for spectral bias

“…To correctly determine the black hole mass and accretion rate for high-redshift quasars, we need more near-IR spectroscopic surveys to facilitate direct checks using the H𝛽 line. In the future, the Gemini Near-Infrared Spectrograph-Distant Quasar Survey (Matthews et al 2021) will provide a large, uniformly distributed sample of quasars at high redshift. It will provide measurements of H𝛽, Fe , [O ], and other UV lines that fall in the near-IR regions.…”