The effects of continuum fitting on Lyman-$\alpha$ forest correlations

TL;DR

This paper investigates how continuum fitting affects Lyman-alpha forest correlation measurements, demonstrating that the distortion matrix technique reliably preserves BAO peak positions while highlighting potential biases in bias parameter estimation.

Contribution

It evaluates and improves the distortion matrix technique for continuum fitting effects in Lyman-alpha forest analyses, ensuring accurate BAO measurements.

Findings

The distortion matrix technique accurately preserves BAO peak positions.

Percent-level biases may affect forest bias parameters.

Proposed modifications improve the technique's robustness.

Abstract

Correlations of fluctuations of the flux in Lyman-$\alpha$ forests of high-redshift quasars have been observed by the Baryonic Acoustic Oscillation Spectroscopy Survey (BOSS) and the Dark Energy Spectroscopy Instrument (DESI) survey where they have revealed the effects of baryon acoustic oscillations (BAO). In order to fit the correlation functions to a physical model and thereby constrain cosmological parameters, it is necessary to take into account the effects of fitting the observed spectra to a template about which the fluctuations are measured. In this paper we use mock spectra to test the distortion matrix technique that has been used since the final BOSS data release to appropriately distort the models. We show that while percent-level effects on the derived forest bias parameters may be present, the technique works sufficiently well that the determination of the BAO peak position is not affected at the percent level. We introduce modifications in the technique used by DESI that were not in the original applications and suggest further possibilities for improvements.