The Target-selection Pipeline for the Dark Energy Spectroscopic Instrument
Adam D. Myers, John Moustakas, Stephen Bailey, Benjamin A. Weaver, Andrew P. Cooper, Jaime E. Forero-Romero, Bela Abolfathi, David M. Alexander, David Brooks, Edmond Chaussidon, Chia-Hsun Chuang, Kyle Dawson, Arjun Dey, Biprateep Dey, Govinda Dhungana, Peter Doel, Kevin Fanning, Enrique Gaztañaga, Satya Gontcho A Gontcho, Alma X. Gonzalez-Morales, ChangHoon Hahn, Hiram K. Herrera-Alcantar, Klaus Honscheid, Mustapha Ishak, Tanveer Karim, David Kirkby, Theodore Kisner, Sergey E. Koposov, Anthony Kremin, Ting-Wen Lan, Martin Landriau, Dustin Lang, Michael E. Levi, Christophe Magneville, Lucas Napolitano, Paul Martini, Aaron Meisner, Jeffrey A. Newman, Nathalie Palanque-Delabrouille, Will Percival, Claire Poppett, Francisco Prada, Anand Raichoor, Ashley J. Ross, Edward F. Schlafly, David Schlegel, Michael Schubnell, Ting Tan, Gregory Tarle, Michael J. Wilson, Christophe Yèche, Rongpu Zhou, Zhimin Zhou, Hu Zou
TL;DR
DESI targets are selected through a imaging-driven, bitmask-based pipeline called desitarget, which encodes target-class membership with 64-bit bitmasks (DESI_TARGET) and tracks sources with a unique TARGETID; bit positions such as $2^{0}$ for LRG and $2^{1}$ for ELG enable complex selections, with a composite mask like $1152921504606849827$ representing multiple target classes, including Bright Galaxy Survey membership. The paper details the data model, file structures, and public code access, and situates desitarget within the broader DESI workflow that includes calibration targets and secondary programs. It documents the phased targeting approach—Commissioning (CMX), Survey Validation (SV1–SV3), and the Main Survey—along with procedures for end-to-end validation, MTLs, and completeness benchmarks. Overall, the work provides a rigorous, reproducible framework for DESI target selection and data products, underpinning reliable large-scale structure and Galactic science from the survey.
Abstract
In 2021 May, the Dark Energy Spectroscopic Instrument (DESI) began a 5 yr survey of approximately 50 million total extragalactic and Galactic targets. The primary DESI dark-time targets are emission line galaxies (ELGs), luminous red galaxies (LRGs) and quasars (QSOs). In bright time, DESI will focus on two surveys known as the Bright Galaxy Survey (BGS) and the Milky Way Survey (MWS). DESI also observes a selection of "secondary" targets for bespoke science goals. This paper gives an overview of the publicly available pipeline (desitarget) used to process targets for DESI observations. Highlights include details of the different DESI survey targeting phases, the targeting ID (TARGETID) used to define unique targets, the bitmasks used to indicate a particular type of target, the data model and structure of DESI targeting files, and examples of how to access and use the desitarget code base. This paper will also describe "supporting" DESI target classes, such as standard stars, sky locations, and random catalogs that mimic the angular selection function of DESI targets. The DESI target selection pipeline is complex and sizable; this paper attempts to summarize the most salient information required to understand and work with DESI targeting data.