Target Selection and Validation of DESI Quasars

By E. Chaussidon, C. Yéche, N. Palanque-Delabrouille, D. M. Alexander, Jinyi Yang, S. Ahlen, S. Bailey, D. Brooks, Zheng Cai, S. Chabanier and 47 more. Astrophysical Journal, 2022

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The Dark Energy Spectroscopic Instrument (DESI) survey will measure large-scale structures using quasars as direct tracers of dark matter in the redshift range 0.9 < z < 2.1 and using Lyα forests in quasar spectra at z > 2.1. We present several methods to select candidate quasars for DESI, using input photometric imaging in three optical bands (g, r, z) from the DESI Legacy Imaging Surveys and two infrared bands (W1, W2) from the Wide-field Infrared Survey Explorer. These methods were extensively tested during the Survey Validation of DESI. In this paper, we report on the results obtained with the different methods and present the selection we optimized for the DESI main survey. The final quasar target selection is based on a random forest algorithm and selects quasars in the magnitude range of 16.5 < r < 23. Visual selection of ultra-deep observations indicates that the main selection consists of 71% quasars, 16% galaxies, 6% stars, and 7% inconclusive spectra. Using the spectra based on this selection, we build an automated quasar catalog that achieves a fraction of true QSOs higher than 99% for a nominal effective exposure time of ∼1000 s. With a 310 deg−2 target density, the main selection allows DESI to select more than 200 deg−2 quasars (including 60 deg−2 quasars with z > 2.1), exceeding the project requirements by 20%. The redshift distribution of the selected quasars is in excellent agreement with quasar luminosity function predictions.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/e06336f704c320a857867577195aba645edb7349

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Citations in the corpus

The Optical Corrector for the Dark Energy Spectroscopic Instrument (2023, background): “The survey will observe four classes of galactic targets: Bright Galaxy Survey targets (BGS, Hahn et al. 2022), luminous red galaxies (LRG, Zhou et al. 2023), emission line galaxies (ELG, Raichoor et al. 2023), and quasi-stellar objects (QSO, Chaussidon et al. 2023).”
Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument (2023, methodology): “A full description of the final target selection algorithms for the LRG, ELG, and quasar samples can be found in accompanying papers by Zhou et al. (2023), Raichoor et al. (2023a), and Chaussidon et al. (2023), respectively.”
Data Release 1 of the Dark Energy Spectroscopic Instrument (2025, unknown): “…( 0 < z < 0.6; O. Ruiz-Macias et al. 2020; C. Hahn et al. 2023 ) ; luminous red galaxies ( LRGs; 0.4 < z < 1.1; R. Zhou et al. 2020, 2023 ) ; emission-line galaxies ( ELGs; 0.6 < z < 1.6; A. Raichoor et al. 2020, 2023 ) ; and QSOs ( 0.9 < z < 4; C. Yèche et al. 2020; E. Chaussidon et al. 2023 ) .”
The Early Data Release of the Dark Energy Spectroscopic Instrument (2023, methodology): “Targets consistent with the “ bluer ” colors of existing DESI quasar targets ( Chaussidon et al. 2023 ) were removed, producing a sample of ∼ 41,000 QSO _ RED targets over the DESI footprint ( ∼ 3 deg − 2 ) .”
The DESI Bright Galaxy Survey: Final Target Selection, Design, and Validation (2022, background): “Complementary papers describe the target selection for the dark-time DESI tracers (LRGs; Zhou et al. 2023; ELGs; A. Raichoor et al. 2023, in preparation; and QSOs; Chaussidon et al. 2023) and the Milky Way Survey (MWS; Cooper et al. 2023).”
Survey Operations for the Dark Energy Spectroscopic Instrument (2023, background): “The primary targets are quasars (Yèche et al. 2020; Chaussidon et al. 2023), emission line galaxies with 0.6 < z < 1.6 (Raichoor et al. 2020, 2023), luminous red galaxies with 0.4 < z < 1 (Zhou et al. 2020, 2023), bright galaxies with z < 0.4 (Ruiz-Macias et al. 2020; Hahn et al. 2022), and stars…”