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The Dark Energy Spectroscopic Instrument (DESI)

Michael E. Levi, Lori E. Allen, Anand Raichoor, Charles Baltay, Segev BenZvi, Florian Beutler, Adam Bolton, Francisco J. Castander, Chia-Hsun Chuang, Andrew Cooper, Jean-Gabriel Cuby, Arjun Dey, Daniel Eisenstein, Xiaohui Fan, Brenna Flaugher, Carlos Frenk, Alma X. Gonzalez-Morales, Or Graur, Julien Guy, Salman Habib, Klaus Honscheid, Stephanie Juneau, Jean-Paul Kneib, Ofer Lahav, Dustin Lang, Alexie Leauthaud, Betta Lusso, Axel de la Macorra, Marc Manera, Paul Martini, Shude Mao, Jeffrey A. Newman, Nathalie Palanque-Delabrouille, Will J. Percival, Carlos Allende Prieto, Constance M. Rockosi, Vanina Ruhlmann-Kleider, David Schlegel, Hee-Jong Seo, Yong-Seon Song, Greg Tarle, Risa Wechsler, David Weinberg, Christophe Yeche, Ying Zu

TL;DR

DESI aims to map dark energy by conducting a large, wide-field spectroscopic survey. The paper documents the instrument design, construction status, survey design, and science goals for 2020–2025, including 34 million redshifts over 14,000 deg$^2$ and target classes like LRGs, ELGs, and QSOs to measure BAO and redshift-space distortions. It also discusses post-2025 options, potential science expansions (e.g., Ly$ m ext{-}$α forest, Milky Way spectroscopy), and the operational and funding considerations for sustaining the facility. The work emphasizes DESI as a leading, US-led wide-field spectroscopic facility that complements imaging surveys and remains crucial for cosmology.

Abstract

We present the status of the Dark Energy Spectroscopic Instrument (DESI) and its plans and opportunities for the coming decade. DESI construction and its initial five years of operations are an approved experiment of the US Department of Energy and is summarized here as context for the Astro2020 panel. Beyond 2025, DESI will require new funding to continue operations. We expect that DESI will remain one of the world's best facilities for wide-field spectroscopy throughout the decade. More about the DESI instrument and survey can be found at https://www.desi.lbl.gov.

The Dark Energy Spectroscopic Instrument (DESI)

TL;DR

DESI aims to map dark energy by conducting a large, wide-field spectroscopic survey. The paper documents the instrument design, construction status, survey design, and science goals for 2020–2025, including 34 million redshifts over 14,000 deg and target classes like LRGs, ELGs, and QSOs to measure BAO and redshift-space distortions. It also discusses post-2025 options, potential science expansions (e.g., Lyα forest, Milky Way spectroscopy), and the operational and funding considerations for sustaining the facility. The work emphasizes DESI as a leading, US-led wide-field spectroscopic facility that complements imaging surveys and remains crucial for cosmology.

Abstract

We present the status of the Dark Energy Spectroscopic Instrument (DESI) and its plans and opportunities for the coming decade. DESI construction and its initial five years of operations are an approved experiment of the US Department of Energy and is summarized here as context for the Astro2020 panel. Beyond 2025, DESI will require new funding to continue operations. We expect that DESI will remain one of the world's best facilities for wide-field spectroscopy throughout the decade. More about the DESI instrument and survey can be found at https://www.desi.lbl.gov.

Paper Structure

This paper contains 2 sections, 4 figures, 2 tables.

Table of Contents

  1. An Overview of DESI: 2020-2025
  2. Beyond 2025 with DESI

Figures (4)

  • Figure 1: The first of 10 focal plate petals installed at the Mayall prime focus (June 26, 2019).
  • Figure 2: Six of the ten 3-armed DESI spectrographs, installed in their thermal enclosure.
  • Figure 3: Measured resolution of the six installed spectrographs. Dotted lines are the system requirements. The as-built results match exquisitely to the modeled performance.
  • Figure 4: The planned DESI survey footprint is shown by the shaded area; it is built on several existing imaging surveys and extends as far south as $\delta=-20^\circ$ in the SGC and $-10^\circ$ in the NGC.