The Gemini Near-Infrared Spectrograph - 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. The GNIRS-DQS survey has 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 from luminous quasars at these redshifts. The measurements 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, whose analysis will greatly benefit from the information garnered in this Gemini Legacy program.

Figure: At sufficiently high redshifts several prominent quasar emission features (white solid lines) are no longer detectable in the optical 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, enable us to establish connections between optical and ultraviolet indicators of fundamental quasar properties while more than doubling the statistics at such high redshifts.

Data Release

This survey comprises 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. They are accessible through the Data Lab file service.

  • 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:

    objSDSS designation
    ra, decRight ascension, Declination in degrees
    zsysSystemic 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 are organized into bunches that represent information about one emission line (Halpha = ha, Hbeta = hb, Mg II = mg2, O III = o3, Fe II = fe2):

    lc_*Line center
    low_lc_*Lower uncertainty in line center
    upp_lc_*Upper uncertainty in line center
    low_fwhm_*Lower uncertainty in FWHM
    upp_fwhm_*Upper uncertainty in FWHM
    ew_*Equivalent width
    low_ew_*Lower uncertainty in equivalent width
    upp_ew_*Upper uncertainty in equivalent width
    as_*Asymmetry of the double Gaussian profile
    kurt_*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 by Matthews et al. (2021), ApJS, 252, 15. 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 paper ( For questions about GNIRS-DQS please contact Brandon Matthews (BrandonMatthews at

Data Access

The GNIRS-DQS data are accessible through several means:

Data Lab Table Access Protocol (TAP) service

TAP provides a convenient access layer for the GNIRS-DQS catalog database tables. TAP-aware clients (such as TOPCAT) can point to, select the gnirs_dqs database, and see the database tables and descriptions. Descriptions of the associate tables can also be found on the Data Lab table browser.

Data Lab Query Manager

The Query Manager is available as part of the Data Lab software distribution. The Query Manager client provides a Python API to Data Lab database services. These services include anonymous access through synchronous queries of the catalog made directly to the database as well as authenticated access, asynchronous queries, personal database storage, and storage through the Data Lab VOSpace.

Jupyter Notebook Server

An example Jupyter Notebook for accessing GNIRS-DQS data from Data Lab can be found on our GitHub page here. You can also access this notebook and our other science example notebooks through the Data Lab Jupyter Notebook server (user authenticated service).