Angular clustering properties of the DESI QSO target selection using DR9 Legacy Imaging Surveys

Edmond Chaussidon, Christophe Yèche, Nathalie Palanque-Delabrouille, Arnaud De Mattia, Adam D. Myers, Mehdi Rezaie, Ashley J. Ross, Hee Jong Seo, David Brooks, Enrique Gaztañaga, Robert Kehoe, Michael E. Levi, Jeffrey A. Newman, Gregory Tarlé, Kai Zhang

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The quasar target selection for the upcoming survey of the Dark Energy Spectroscopic Instrument (DESI) will be fixed for the next 5 yr. The aim of this work is to validate the quasar selection by studying the impact of imaging systematics as well as stellar and galactic contaminants, and to develop a procedure to mitigate them. Density fluctuations of quasar targets are found to be related to photometric properties such as seeing and depth of the Data Release 9 of the DESI Legacy Imaging Surveys. To model this complex relation, we explore machine learning algorithms (random forest and multilayer perceptron) as an alternative to the standard linear regression. Splitting the footprint of the Legacy Imaging Surveys into three regions according to photometric properties, we perform an independent analysis in each region, validating our method using extended Baryon Oscillation Spectroscopic Survey (eBOSS) EZ-mocks. The mitigation procedure is tested by comparing the angular correlation of the corrected target selection on each photometric region to the angular correlation function obtained using quasars from the Sloan Digital Sky Survey (SDSS) Data Release 16. With our procedure, we recover a similar level of correlation between DESI quasar targets and SDSS quasars in two-thirds of the total footprint and we show that the excess of correlation in the remaining area is due to a stellar contamination that should be removed with DESI spectroscopic data. We derive the Limber parameters in our three imaging regions and compare them to previous measurements from SDSS and the 2dF QSO Redshift Survey.

Original languageEnglish
Pages (from-to)3904-3923
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date10 Nov 2021
Publication statusPublished - 1 Jan 2022


  • cosmology: observations
  • large-scale structure of Universe
  • methods: data analysis
  • surveys

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