3D Correlations in the Lyman-$\alpha$ Forest from Early DESI Data

TL;DR

This paper reports the first measurements of Lyman-alpha forest correlations from early DESI data, detecting the BAO peak and validating analysis methods for future large-scale cosmological measurements.

Contribution

It presents initial Ly$ ext{α}$ correlation measurements from DESI, demonstrating consistency with previous surveys and preparing for future BAO scale analysis.

Findings

Detected BAO peak with 3.8σ significance

Measurements are consistent with eBOSS results

Uncertainties are only 1.7 times larger than final eBOSS data

Abstract

We present the first measurements of Lyman-$\alpha$ (Ly$\alpha$) forest correlations using early data from the Dark Energy Spectroscopic Instrument (DESI). We measure the auto-correlation of Ly$\alpha$ absorption using 88,509 quasars at $z>2$, and its cross-correlation with quasars using a further 147,899 tracer quasars at $z\gtrsim1.77$. Then, we fit these correlations using a 13-parameter model based on linear perturbation theory and find that it provides a good description of the data across a broad range of scales. We detect the BAO peak with a signal-to-noise ratio of $3.8\sigma$, and show that our measurements of the auto- and cross-correlations are fully-consistent with previous measurements by the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). Even though we only use here a small fraction of the final DESI dataset, our uncertainties are only a factor of 1.7 larger than those from the final eBOSS measurement. We validate the existing analysis methods of Ly$\alpha$ correlations in preparation for making a robust measurement of the BAO scale with the first year of DESI data.