DESI 2024 III: Baryon Acoustic Oscillations from Galaxies and Quasars (2404.03000v1)

Abstract: We present the DESI 2024 galaxy and quasar baryon acoustic oscillations (BAO) measurements using over 5.7 million unique galaxy and quasar redshifts in the range 0.1<z<2.1. Divided by tracer type, we utilize 300,017 galaxies from the magnitude-limited Bright Galaxy Survey with 0.1<z<0.4, 2,138,600 Luminous Red Galaxies with 0.4<z<1.1, 2,432,022 Emission Line Galaxies with 0.8<z<1.6, and 856,652 quasars with 0.8<z<2.1, over a ~7,500 square degree footprint. The analysis was blinded at the catalog-level to avoid confirmation bias. All fiducial choices of the BAO fitting and reconstruction methodology, as well as the size of the systematic errors, were determined on the basis of the tests with mock catalogs and the blinded data catalogs. We present several improvements to the BAO analysis pipeline, including enhancing the BAO fitting and reconstruction methods in a more physically-motivated direction, and also present results using combinations of tracers. We present a re-analysis of SDSS BOSS and eBOSS results applying the improved DESI methodology and find scatter consistent with the level of the quoted SDSS theoretical systematic uncertainties. With the total effective survey volume of ~ 18 Gpc$^3$, the combined precision of the BAO measurements across the six different redshift bins is ~0.52%, marking a 1.2-fold improvement over the previous state-of-the-art results using only first-year data. We detect the BAO in all of these six redshift bins. The highest significance of BAO detection is $9.1\sigma$ at the effective redshift of 0.93, with a constraint of 0.86% placed on the BAO scale. We find our measurements are systematically larger than the prediction of Planck-2018 LCDM model at z<0.8. We translate the results into transverse comoving distance and radial Hubble distance measurements, which are used to constrain cosmological models in our companion paper [abridged].

Astrophysical Insights from DESI's Baryon Acoustic Oscillation Measurements

The paper "DESI 2024 III: Baryon Acoustic Oscillations from Galaxies and Quasars" presents the findings of the Dark Energy Spectroscopic Instrument (DESI) Collaboration regarding the measurement of baryon acoustic oscillations (BAO) using a comprehensive dataset of galaxies and quasars. The research utilizes over 5.7 million redshift measurements across a significant redshift range, providing a robust dataset for cosmological analysis. This work marks a substantial contribution to our understanding of cosmic distances and the expansion history of the universe.

Methodology

The DESI collaboration conducted a blinded analysis to mitigate confirmation bias, a novel approach in the context of BAO studies. This precaution ensured that the results were not influenced by prior expectations. The paper describes significant advancements in the BAO analysis pipeline, focusing on physically motivated enhancements to the fitting and reconstruction methodologies. The paper employs a unified BAO analysis across various tracers, implementing a sophisticated model that includes galaxy and quasar redshifts divided into distinct samples based on redshift range and galaxy type.

Key Results

The DESI dataset, with an effective survey volume of approximately 18 Gpc³, offers high precision in measuring BAO features across six redshift bins. The BAO detection achieves a significance of up to 9.1σ, specifically at an effective redshift of 0.93. The constraints on the BAO scale bring notable refinement over previous studies. The analysis detects BAO across all redshift bins with an impressive precision, marked by a 0.86% constraint on the BAO scale at a median redshift.

Systematic Error Handling

The researchers undertook extensive tests using mock catalogs to assess both systematic and statistical errors, ensuring the robustness of the derived cosmological parameters. The selection function and survey geometry were systematically accounted for using matched random samples. Moreover, a comprehensive systematic error budget was developed to encompass theoretical, modeling, and observational inaccuracies.

Comparisons and Implications

This paper compares the DESI results with previous measurements from BOSS, eBOSS, and other significant surveys, demonstrating a marked improvement in precision. However, certain discrepancies, particularly in low redshift ranges, suggest potential insights into the underlying cosmological model, challenging the ΛCDM framework at specific redshift intervals.

Future Scope

The results of the DESI survey indicate its expected impact on upcoming cosmological analyses, especially regarding dark energy characterizations and the Hubble tension. The dataset provides a foundation for further analysis, potentially revealing new aspects of cosmic structure formation and evolution.

The paper concludes by emphasizing the importance of the DESI measurements in the broader context of cosmological research. The methodologies and results set a precedent for future spectroscopic surveys aiming for even higher precision in mapping the universe's structure and expansion history.