DESI DR1 Ly{\alpha} 1D power spectrum: The Fast Fourier Transform estimator measurement

TL;DR

This paper reports a highly precise measurement of the one-dimensional Lyman-alpha forest power spectrum from DESI DR1 data using a Fast Fourier Transform estimator, improving noise characterization and uncertainty estimation.

Contribution

It introduces a validated FFT-based estimator for the Lyman-alpha power spectrum, with enhanced noise and covariance analysis, and compares results to previous measurements.

Findings

Most precise 1D Lyman-alpha power spectrum measurement to date

Consistent with previous DESI early data release results

Improved noise and covariance estimation methods

Abstract

We present the one-dimensional Lyman-$\alpha$ forest power spectrum measurement derived from the data release 1 (DR1) of the Dark Energy Spectroscopic Instrument (DESI). The measurement of the Lyman-$\alpha$ forest power spectrum along the line of sight from high-redshift quasar spectra provides information on the shape of the linear matter power spectrum, neutrino masses, and the properties of dark matter. In this work, we use a Fast Fourier Transform (FFT)-based estimator, which is validated on synthetic data in a companion paper. Compared to the FFT measurement performed on the DESI early data release, we improve the noise characterization with a cross-exposure estimator and test the robustness of our measurement using various data splits. We also refine the estimation of the uncertainties and now present an estimator for the covariance matrix of the measurement. Furthermore, we compare our results to previous high-resolution and eBOSS measurements. In another companion paper, we present the same DR1 measurement using the Quadratic Maximum Likelihood Estimator (QMLE). These two measurements are consistent with each other and constitute the most precise one-dimensional power spectrum measurement to date, while being in good agreement with results from the DESI early data release.