The DESI Experiment Part I: Science,Targeting, and Survey Design

TL;DR

The DESI experiment is a comprehensive ground-based survey designed to map the universe's large-scale structure through spectroscopic observations of galaxies and quasars, aiming to understand dark energy and cosmic expansion.

Contribution

This paper details the design, target selection, and survey strategy of DESI, a new Stage IV dark energy experiment utilizing multiple galaxy and quasar classes for cosmological measurements.

Findings

Over 30 million galaxy and quasar redshifts will be obtained.

DESI will measure baryon acoustic oscillations and growth of structure.

The survey will include a Bright Galaxy Survey during moonlit nights.

Abstract

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1.0$. To probe the Universe out to even higher redshift, DESI will target bright [O II] emission line galaxies up to $z=1.7$. Quasars will be targeted both as direct tracers of the underlying dark matter distribution and, at higher redshifts ($ 2.1 < z < 3.5$), for the Ly-$\alpha$ forest absorption features in their spectra, which will be used to trace the distribution of neutral hydrogen. When moonlight prevents efficient observations of the faint targets of the baseline survey, DESI will conduct a magnitude-limited Bright Galaxy Survey comprising approximately 10 million galaxies with a median $z\approx 0.2$. In total, more than 30 million galaxy and quasar redshifts will be obtained to measure the BAO feature and determine the matter power spectrum, including redshift space distortions.