Overview of the Instrumentation for the Dark Energy Spectroscopic Instrument

Abstract

The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z > 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector; a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface; 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs; and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii] doublet at 8 × 10−17 erg s−1 cm−2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned.

Target Selection and Validation of DESI Emission Line Galaxies

“…The DESI instrument, which is described in detail in DESI Collaboration et al (2016b) and Abareshi et al (2022), is a multi-spectroscopic instrument that is mounted at the prime focus of the 4 m Mayall Telescope at Kitt Peak, Arizona. The focal plane covers a field of view of about 8 deg 2 (T. Miller 2023, in preparation), and it is equipped with 5000 fiber positioners (Silber et al 2022), distributed in ten "petals."…”

The DESI Survey Validation: Results from Visual Inspection of Bright Galaxies, Luminous Red Galaxies, and Emission-line Galaxies

“…The data used in this work was obtained by the DESI instrumentation with a 3°.2 diameter field of view and 5020 robotic fiber positioners installed on the 4 m Mayall Telescope at Kitt Peak National Observatory (Abareshi et al 2022;T. Miller et al 2023, in preparation;Silber et al 2023).…”

Target Selection and Validation of DESI Quasars

“…The Dark Energy Spectroscopic Instrument (DESI; Levi et al 2013;DESI Collaboration et al 2016a, 2016bAbareshi et al 2022) survey will measure with high precision the baryon acoustic feature imprinted on the large-scale structure of the universe, as well as the distortions of galaxy clustering due to redshift-space effects. To achieve these goals, the survey will make spectroscopic observations of four distinct classes of extragalactic sources-nearby bright galaxies (Ruiz-Macias et al 2020), luminous red galaxies (Zhou et al 2020), starforming emission line galaxies (Raichoor et al 2020), and quasars (Yèche et al 2020).…”