Target Selection and Validation of DESI Quasars
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 Ly-alpha 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 Explorer (WISE). 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 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 >99% purity for a nominal effective exposure time of ~1000s. With a 310 per sq. deg. target density, the main selection allows DESI to select more than 200 QSOs per sq. deg. (including 60 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.
Cite
@article{arxiv.2208.08511,
title = {Target Selection and Validation of DESI Quasars},
author = {Edmond Chaussidon and Christophe Yèche and Nathalie Palanque-Delabrouille and David M. Alexander and Jinyi Yang and Steven Ahlen and Stephen. Bailey and David Brooks and Zheng Cai and Solène Chabanier and Tamara M. Davis and Kyle Dawson and Axel de la Macorra and Arjun Dey and Biprateep Dey and Sarah Eftekharzadeh and Daniel J. Eisenstein and Kevin Fanning and Andreu Font-Ribera and Enrique Gaztañaga and Satya Gontcho A Gontcho and Alma X. Gonzalez-Morales and Julien Guy and Hiram K. Herrera-Alcantar and Klaus Honscheid and Mustapha Ishak and Linhua Jiang and Stephanie Juneau and Robert Kehoe and Theodore Kisner and Andras Kovács and Anthony Kremin and Ting-Wen Lan and Martin Landriau and Laurent Le Guillou and Michael E. Levi and Christophe Magneville and Paul Martini and Aaron M. Meisner and John Moustakas and Andrea Muñoz-Gutiérrez and Adam D. Myers and Jeffrey A. Newman and Jundan Nie and Will J. Percival and Claire Poppett and Francisco Prada and Anand Raichoor and Corentin Ravoux and Ashley J. Ross and Edward Schlafly and David Schlegel and Ting Tan and Gregory Tarlé and Rongpu Zhou and Zhimin Zhou and Hu Zou},
journal= {arXiv preprint arXiv:2208.08511},
year = {2023}
}
Comments
21 pages, 21 figures, typos corrected, references added