The DESI Experiment Part I: Science,Targeting, and Survey Design (1611.00036v2)

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.

• The paper presents a pioneering survey design that will map over 30 million galaxy and quasar redshifts to measure cosmic expansion using BAO and redshift distortions.
• It outlines a robust methodology leveraging multiple target classes, including a bright galaxy survey under variable observing conditions.
• DESI's results are expected to impose stringent constraints on dark energy models and enhance our understanding of cosmic structure and evolution.

Analysis of the DESI Experiment: Science, Targeting, and Survey Design

The paper in discussion presents a comprehensive overview of the Dark Energy Spectroscopic Instrument (DESI) project, which represents a significant advancement in the field of cosmological studies. As a Stage IV ground-based dark energy experiment, DESI aims to explore the intricacies of dark energy through detailed analysis of baryon acoustic oscillations (BAO) and redshift-space distortions. The following essay provides an in-depth examination of DESI’s objectives, methodology, and anticipated contributions to our understanding of the universe’s expansion.

Objectives and Methodology

The primary objective of DESI is to elucidate the nature of dark energy by precisely mapping the distribution of galaxies and quasars across a significant portion of the sky. The project seeks to leverage BAO as a standard ruler to measure cosmic distances and analyze the universe's expansion history. Additionally, DESI examines the growth of large-scale structure through redshift-space distortions, providing an indirect measure of the effects of gravity on cosmic scales.

DESI’s methodology involves a wide-area galaxy and quasar redshift survey. The scope of the survey includes four primary target classes derived from imaging data: luminous red galaxies up to a redshift of $z=1.0$, [O emission line galaxies up to $z=1.7$, and quasars, which serve dual purposes as tracers of the dark matter distribution and as providers of Ly-α absorption features for discerning neutral hydrogen distribution at redshifts $2.1 < z < 3.5$.

Survey Design

The survey design of DESI is methodically structured to accommodate varying observational conditions. During periods of bright moonlight, DESI will conduct a Bright Galaxy Survey with a magnitude-limited sample to ensure constant data acquisition. This survey will encompass approximately 10 million galaxies with a median redshift $z \approx 0.2$, supplementing the baseline survey data. Over the course of the project, DESI is projected to compile over 30 million galaxy and quasar redshifts, enabling robust measurement of the BAO feature and the matter power spectrum, incorporating redshift space distortions.

Implications and Speculation

The anticipated results from DESI have profound implications for cosmology and theoretical physics. By achieving precise measurements of cosmic distances and the matter power spectrum, DESI is poised to place stringent constraints on models of dark energy, potentially challenging or refining our understanding of its nature. Moreover, the comprehensive dataset obtained through the DESI survey will serve as a valuable resource for cross-disciplinary analyses, informing theories related to dark matter, gravitation, and the large-scale structure of the universe.

Speculatively, the methodologies and technical advancements developed through the DESI project could inform future cosmic surveys, both ground-based and space-borne, ensuring a legacy of innovation and inquiry in cosmological research.

Conclusion

DESI stands as a monumental effort in the exploration of the universe’s expansion and its underlying forces, promising to augment our grasp of cosmological phenomena through meticulous design and robust data collection. By targeting a vast array of cosmological indicators and employing a structured survey design, DESI is well-positioned to contribute substantially to the scientific community’s understanding of dark energy and the universe at large. As future developments unfold, DESI’s findings are expected to resonate across multiple domains in astrophysics, fostering an era of discovery and insight.