DESI 2024 III: baryon acoustic oscillations from galaxies and quasars

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 employ a unified BAO analysis method across all
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 Gpc3, 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 9.1σ at
the effective redshift of 0.93, with a constraint of 0.86% placed on the BAO scale. We find
that our observed BAO scales are systematically larger than the prediction of the
Planck 2018-ΛCDM 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.