The Dark Energy Spectroscopic Instrument: one-dimensional power spectrum from first Ly α forest samples with Fast Fourier Transform

We present the one-dimensional Ly alpha forest power spectrum measurement using the first data provided by the Dark Energy Spectroscopic Instrument (DESI). The data sample comprises 26 330 quasar spectra, at redshift z > 2.1, contained in the DESI Early Data Release and the first 2 months of the main survey. We employ a Fast Fourier Transform (FFT) estimator and compare the resulting power spectrum to an alternative likelihood-based method in a companion paper. We investigate methodological and instrumental contaminants associated with the new DESI instrument, applying techniques similar to previous Sloan Digital Sky Survey (SDSS) measurements. We use synthetic data based on lognormal approximation to validate and correct our measurement. We compare our resulting power spectrum with previous SDSS and high-resolution measurements. With relatively small number statistics, we successfully perform the FFT measurement, which is already competitive in terms of the scale range. At the end of the DESI survey, we expect a five times larger Ly alpha forest sample than SDSS, providing an unprecedented precise one-dimensional power spectrum measurement.

Automated summary

This paper presents the measurement of the one-dimensional Ly alpha forest power spectrum using data from the Dark Energy Spectroscopic Instrument (DESI). The measurement is based on the first 2 months of the main survey and employs a Fast Fourier Transform (FFT) estimator. Validation of the measurement is done using synthetic data and the results show that the Ly alpha forest sample obtained from the DESI survey will be five times larger than that from the previous Sloan Digital Sky Survey (SDSS).