DESI DR2 results. I. Baryon acoustic oscillations from the Lyman alpha forest
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Bibliographic record
Abstract
We present the baryon acoustic oscillation (BAO) measurements with the Lyman-<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>α</a:mi></a:math> (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>Ly</c:mi><c:mi>α</c:mi></c:math>) forest from the second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI) survey. Our BAO measurements include both the autocorrelation of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>Ly</e:mi><e:mi>α</e:mi></e:math> forest absorption observed in the spectra of high-redshift quasars and the cross-correlation of the absorption with the quasar positions. The total sample size is approximately a factor of 2 larger than the DR1 dataset, with forest measurements in over 820,000 quasar spectra and the positions of over 1.2 million quasars. We describe several significant improvements to our analysis in this paper, and two supporting papers describe improvements to the synthetic datasets that we use for validation and how we identify damped <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>Ly</g:mi><g:mi>α</g:mi></g:math> absorbers. Our main result is that we have measured the BAO scale with a statistical precision of 1.1% along and 1.3% transverse to the line of sight, for a combined precision of 0.65% on the isotropic BAO scale at <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>z</i:mi><i:mi>eff</i:mi></i:msub><i:mo>=</i:mo><i:mn>2.33</i:mn></i:math>. This excellent precision, combined with recent theoretical studies of the BAO shift due to nonlinear growth, motivated us to include a systematic error term in <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>Ly</k:mi><k:mi>α</k:mi></k:math> BAO analysis for the first time. We measure the ratios <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:msub><m:mi>D</m:mi><m:mi>H</m:mi></m:msub><m:mo stretchy="false">(</m:mo><m:msub><m:mi>z</m:mi><m:mi>eff</m:mi></m:msub><m:mo stretchy="false">)</m:mo><m:mo>/</m:mo><m:msub><m:mi>r</m:mi><m:mi>d</m:mi></m:msub><m:mo>=</m:mo><m:mn>8.632</m:mn><m:mo>±</m:mo><m:mn>0.098</m:mn><m:mo>±</m:mo><m:mn>0.026</m:mn></m:math> and <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msub><q:mi>D</q:mi><q:mi>M</q:mi></q:msub><q:mo stretchy="false">(</q:mo><q:msub><q:mi>z</q:mi><q:mi>eff</q:mi></q:msub><q:mo stretchy="false">)</q:mo><q:mo>/</q:mo><q:msub><q:mi>r</q:mi><q:mi>d</q:mi></q:msub><q:mo>=</q:mo><q:mn>38.99</q:mn><q:mo>±</q:mo><q:mn>0.52</q:mn><q:mo>±</q:mo><q:mn>0.12</q:mn></q:math>, where <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:msub><u:mi>D</u:mi><u:mi>H</u:mi></u:msub><u:mo>=</u:mo><u:mi>c</u:mi><u:mo>/</u:mo><u:mi>H</u:mi><u:mo stretchy="false">(</u:mo><u:mi>z</u:mi><u:mo stretchy="false">)</u:mo></u:math> is the Hubble distance, <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:msub><y:mi>D</y:mi><y:mi>M</y:mi></y:msub></y:math> is the transverse comoving distance, <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:msub><ab:mi>r</ab:mi><ab:mi>d</ab:mi></ab:msub></ab:math> is the sound horizon at the drag epoch, and we quote both the statistical and the theoretical systematic uncertainty. The companion paper presents the BAO measurements at lower redshifts from the same dataset and the cosmological interpretation.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it