The imprint of sound waves in the primordial plasma survives as a preferred separation between galaxies — a standard ruler roughly 150 Mpc long. Measuring it at a range of redshifts maps the expansion history.
DESI measures it two ways: from the clustering of discrete tracers out to z ≈ 2.1, and from Lyman-α forest absorption at z ≈ 2.3. The cosmological constraints drawn from these measurements are collected under Cosmological Parameter Estimation. Forest catalogs, systematics and the pipeline reference set are on the Lyman-α page.
Key paper · DR2
BAO from three years of DESI data across the full set of tracers — bright galaxies, luminous red galaxies, emission-line galaxies and quasars.
Key paper · DR1
The first-year measurement, whose combination with CMB and supernova data first showed a preference for time-evolving dark energy.
Clustering catalogs and systematics: sample definitions and two-point statistics, BAO reconstruction, fiber-assignment realizations, and halo-occupation systematics for emission-line galaxies.
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The forest reaches z ≈ 2.3, the only DESI probe deep in the matter-dominated era. Both analyses use the forest auto-correlation together with its cross-correlation with quasar positions.
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DESI completed its five-year survey in May 2026. BAO from the full survey is expected in early 2027 and will be added here.