# The Lyman-alpha forest power spectrum from the XQ-100 Legacy Survey

## TL;DR

This paper measures the Lyman-alpha flux power spectrum from the XQ-100 quasar spectra, providing high-redshift data with intermediate resolution and signal-to-noise, useful for cosmological structure formation studies.

## Contribution

First measurement of the Lyman-alpha flux power spectrum from the XQ-100 survey covering redshifts 3-4.2 with detailed uncertainty analysis and comparison to existing literature.

## Key findings

- Results agree with previous measurements in the literature.
- Uncertainties are comparable or smaller than BOSS data, especially at high redshift.
- Data spans high redshift regime, crucial for structure formation models.

## Abstract

We present the Lyman-$\alpha$ flux power spectrum measurements of the XQ-100 sample of quasar spectra obtained in the context of the European Southern Observatory Large Programme "Quasars and their absorption lines: a legacy survey of the high redshift universe with VLT/XSHOOTER". Using $100$ quasar spectra with medium resolution and signal-to-noise ratio we measure the power spectrum over a range of redshifts $z = 3 - 4.2$ and over a range of scales $k = 0.003 - 0.06\,\mathrm{s\,km^{-1}}$. The results agree well with the measurements of the one-dimensional power spectrum found in the literature. The data analysis used in this paper is based on the Fourier transform and has been tested on synthetic data. Systematic and statistical uncertainties of our measurements are estimated, with a total error (statistical and systematic) comparable to the one of the BOSS data in the overlapping range of scales, and smaller by more than $50\%$ for higher redshift bins ($z>3.6$) and small scales ($k > 0.01\,\mathrm{s\,km^{-1}}$). The XQ-100 data set has the unique feature of having signal-to-noise ratios and resolution intermediate between the two data sets that are typically used to perform cosmological studies, i.e. BOSS and high-resolution spectra (e.g. UVES/VLT or HIRES). More importantly, the measured flux power spectra span the high redshift regime which is usually more constraining for structure formation models.