Target Selection and Validation of DESI Quasars
Journal
Astrophysical Journal
Journal Volume
944
Journal Issue
1
Date Issued
2023-02-01
Author(s)
Chaussidon, Edmond
Yèche, Christophe
Palanque-Delabrouille, Nathalie
Alexander, David M.
Yang, Jinyi
Ahlen, Steven
Bailey, Stephen
Brooks, David
Cai, Zheng
Chabanier, Solène
Davis, Tamara M.
Dawson, Kyle
de laMacorra, Axel
Dey, Arjun
Dey, Biprateep
Eftekharzadeh, Sarah
Eisenstein, Daniel J.
Fanning, Kevin
Font-Ribera, Andreu
Gaztañaga, Enrique
A Gontcho, Satya Gontcho
Gonzalez-Morales, Alma X.
Guy, Julien
Herrera-Alcantar, Hiram K.
Honscheid, Klaus
Ishak, Mustapha
Jiang, Linhua
Juneau, Stephanie
Kehoe, Robert
Kisner, Theodore
Kovács, Andras
Kremin, Anthony
Landriau, Martin
Le Guillou, Laurent
Levi, Michael E.
Magneville, Christophe
Martini, Paul
Meisner, Aaron M.
Moustakas, John
Muñoz-Gutiérrez, Andrea
Myers, Adam D.
Newman, Jeffrey A.
Nie, Jundan
Percival, Will J.
Poppett, Claire
Prada, Francisco
Raichoor, Anand
Ravoux, Corentin
Ross, Ashley J.
Schlafly, Edward
Schlegel, David
Tan, Ting
Tarlé, Gregory
Zhou, Rongpu
Zhou, Zhimin
Zou, Hu
Abstract
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.
SDGs
Type
journal article