Placing High-Redshift Quasars in Perspective: The Gemini Near-Infrared Spectroscopic - Distant Quasar Survey (GNIRS-DQS)

Our current understanding of supermassive black hole (SMBH) growth in the distant universe is compromised by the lack of key diagnostic rest-frame optical emission lines in quasar spectra. As a consequence, our view of how SMBHs and their host galaxies mutually coevolve during the peak of quasar activity is biased and incomplete. To this end, we have obtained high-quality GNIRS spectroscopic observations, in the 1.0-2.5 micron band, for a uniform sample of 260 Sloan Digital Sky Survey (SDSS) quasars at redshifts between 1.5 and 3.5. This survey more than doubles the existing inventory of near-infrared spectra of luminous quasars at these redshifts. These measurements will facilitate a more complete understanding of how the rest-frame UV-optical spectral properties depend on redshift and luminosity, and test whether the physical properties of the quasar central engine evolve over cosmic time. The next generation of cosmological surveys will generate millions of optical quasar spectra, the analysis of which will greatly benefit from the information garnered in this investigation, an invaluable Gemini legacy.

Figure: At sufficiently high redshifts, several prominent quasar emission features (white solid lines) are no longer detectable in the optical spectral range, represented here by the SDSS band that extends between approximately 0.4 micron and 1.0 micron (solid black line). For the broad Hβ and narrow [O III] lines that are rich in diagnostic power, this occurs above redshift 1, including the era of fast quasar growth. GNIRS-DQS more than triples the observed spectral band, allowing us to observe these and other emission lines in a uniform sample of 260 SDSS quasars at redshifts between 1.5 (dashed line) and 3.5. The available SDSS spectra of these sources, which cover at least the rest-frame ultraviolet C IV emission line, will enable us to establish connections between optical and ultraviolet indicators of fundamental quasar properties while more than doubling the statistics at such high redshifts.

This survey constitutes spectroscopic measurements for 260 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 (≲19.0 mag, ≲16.5 mag) of Sloan Digital Sky Survey (SDSS) quasars at 1.5 < z < 3.5 with a monochromatic luminosity (λLλ) at 5100Å 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 λ2798, λ2803, Hβ λ4861, and [O III] λ4959, λ5007 emission lines, in each source.

Below see a brief description for the corresponding files associated with the survey:

  • ASCIIs: Each quasar has a corresponding ASCII file containing select data about certain features of the quasar. These ASCII files are broken up into columns, and will have information broken down into the following:

    Column 1: SDSS designation
    Column 2 & 3: Right Ascension and Declination in degrees
    Column 4: Systemic redshift as measured by the best available spectral indicator
    Depending on the existence of certain lines, which is a product of a variety of factors which include things like redshift and noise, the subsequent columns will be organized into bunches that represent information about one emission line:
    1-3 The line center, and corresponding upper and lower error bars
    4-6 The FWHM, and corresponding upper and lower error bars
    7-9 The EW, and corresponding upper and lower error bars
    10 The asymmetry of the double Gaussian profile
    11 The kurtosis of the double Gaussian profile
    Absent emission lines are indicated by a series of zeroes.

  • Data files: These are the csv tables associated with the published version of the GNIRS-DQS survey and redshift analysis paper in ApJ. A description of the tables and their respective formatting can be found in the paper itself.

Descriptions and further information can be found in the corresponding survey papers ( and TBD). For questions, please contact Brandon Matthews (BrandonMatthews at