The Target-selection Pipeline for the Dark Energy Spectroscopic Instrument

TL;DR

This paper describes the design, structure, and usage of the DESI target selection pipeline, which processes and categorizes targets for the Dark Energy Spectroscopic Instrument's extensive survey of galaxies and stars.

Contribution

It provides a comprehensive overview of the DESI target selection pipeline, including data models, target classes, and code access, facilitating research and data analysis.

Findings

Detailed description of DESI survey targeting phases

Explanation of TARGETID and bitmask usage

Guidance on accessing and using the desitarget code

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.