[论文解读] DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest

DESI Collaboration, Munawar Karim+148 more|ArXiv.org|Mar 18, 2025

Galaxies: Formation, Evolution, Phenomena被引用 6

一句话总结

DESI DR2 使用 Lyα 森林的自相关与互相关测量 BAO 尺度，在 z_eff=2.33 时实现 0.65% 的各向同性精度，并包含 Lyα BAO 位移的系统误差项。

ABSTRACT

We present the Baryon Acoustic Oscillation (BAO) measurements with the Lyman-alpha (LyA) forest from the second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI) survey. Our BAO measurements include both the auto-correlation of the LyA 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 two 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 LyA 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 $z_{eff} = 2.33$. 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 LyA BAO analysis for the first time. We measure the ratios $D_H(z_{eff})/r_d = 8.632 \pm 0.098 \pm 0.026$ and $D_M(z_{eff})/r_d = 38.99 \pm 0.52 \pm 0.12$, where $D_H = c/H(z)$ is the Hubble distance, $D_M$ is the transverse comoving distance, $r_d$ 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.

研究动机与目标

• Measure the Baryon Acoustic Oscillation scale from the Lyman-α forest using DESI DR2 data.
• Combine Lyα forest auto-correlation and quasar-forest cross-correlation for BAO extraction.
• Quantify statistical and systematic uncertainties, including nonlinear BAO shift considerations.
• Provide cosmological constraints and place results in the context of full DESI BAO measurements.

提出的方法

• Analyze Lyα forest fluctuations from DESI DR2 spectra using coadded observations to maximize SNR.
• Compute two-point correlation functions for Lyα auto-correlation and Lyα–quasar cross-correlation.
• Model distortion matrices and metal-line contamination to robustly extract BAO signals.
• Fit two-dimensional correlation functions to extract BAO scale parameters with error budgets.
• Report D_H(z_eff)/r_d and D_M(z_eff)/r_d with statistical and theoretical systematic uncertainties.

实验结果

研究问题

• RQ1 What is the BAO scale from the Lyα forest at z_eff ≈ 2.33 as encoded in D_H(z_eff)/r_d and D_M(z_eff)/r_d?
• RQ2 How do Lyα forest auto- and forest–quasar cross-correlations constrain cosmic distances along and across the line of sight?
• RQ3 What are the dominant systematic uncertainties in Lyα BAO measurements, including nonlinear growth shifts and metal contamination?
• RQ4 How do DR2 Lyα BAO results compare with previous Lyα BAO measurements and lower-redshift BAO results within the DESI program?

主要发现

• BAO scale measured with 1.1% statistical precision along the line of sight and 1.3% transverse to the line of sight.
• Isotropic BAO precision of 0.65% at z_eff = 2.33 when combining directions.
• Reported ratios: D_H(z_eff)/r_d = 8.632 ± 0.098(stat) ± 0.026(sys) and D_M(z_eff)/r_d = 38.99 ± 0.52(stat) ± 0.12(sys).
• Inclusion of a systematic error term in Lyα BAO analysis due to nonlinear growth shifts.
• DR2 dataset contains over 820,000 Lyα forest spectra and cross-correlation with more than 1.2 million quasars.