Broadband distortion modeling in Lyman-$\alpha$ forest BAO fitting

Abstract

In recent years, the Lyman-$\alpha$ absorption observed in the spectra of high-redshift quasars has been used as a tracer of large-scale structure by means of the three-dimensional Lyman-$\alpha$ forest auto-correlation function at redshift $z\simeq 2.3$, but the need to fit the quasar continuum in every absorption spectrum introduces a broadband distortion that is difficult to correct and causes a systematic error for measuring any broadband properties. We describe a $k$-space model for this broadband distortion based on a multiplicative correction to the power spectrum of the transmitted flux fraction that suppresses power on scales corresponding to the typical length of a Lyman-$\alpha$ forest spectrum. Implementing the distortion model in fits for the baryon acoustic oscillation (BAO) peak position in the Lyman-$\alpha$ forest auto-correlation, we find that the fitting method recovers the input values of the linear bias parameter $b_F$ and the redshift-space distortion parameter ${\beta }_F$ for mock data sets with a systematic error of less than 0.5\%. Applied to the auto-correlation measured for BOSS Data Release 11, our method improves on the previous treatment of broadband distortions in BAO fitting by providing a better fit to the data using fewer parameters and reducing the statistical errors on ${\beta }_F$ and the combination $b_F(1+{\beta }_F)$ by more than a factor of seven. The measured values at redshift $z=2.3$ are ${\beta }_F=1.39_{-0.10-0.19-0.28}^{+0.11+0.24+0.38}$ and $b_F(1+{\beta }_F)=-0.374_{-0.007-0.014-0.022}^{+0.007+0.013+0.020}$ (1$\sigma$, 2$\sigma$ and 3$\sigma$ statistical errors). Our fitting software and the input files needed to reproduce our main results are publicly available.

28 pages, 15 figures, matches the published version

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• Baryon acoustic oscillations from the cross-correlation of Ly$\alpha$ absorption and quasars in eBOSS DR14
• Elucidating $\Lambda$CDM: Impact of Baryon Acoustic Oscillation Measurements on the Hubble Constant Discrepancy
• Automatic physical inference with information maximising neural networks
• The Non-Linear Power Spectrum of the Lyman Alpha Forest
• The SDSS-DR12 large-scale cross-correlation of Damped Lyman Alpha Systems with the Lyman Alpha Forest
• The role of galaxies and AGN in reionizing the IGM - II: metal-tracing the faint sources of reionization at $5\lesssim z\lesssim 6$
• The cross-correlation between 21cm intensity mapping maps and the Lyman-alpha forest in the post-reionization era
• The VLT LBG Redshift Survey - VI. Mapping HI in the proximity of $z\sim 3$ LBGs with X-Shooter
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• The triply-ionized carbon forest from eBOSS: cosmological correlations with quasars in SDSS-IV DR14
• The Alcock-Paczyński effect from Lyman-$\alpha$ forest correlations: Analysis validation with synthetic data
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• Quasar -- CIV forest cross-correlation with SDSS DR12
• Modeling Lyman-α Forest Cross-Correlations with LyMAS
• Quintessence scalar field and cosmological constant: Dynamics of a multi-component dark energy model
• Reconstructing the Gravitational Lensing Potential from the Lyman-$\alpha$ Forest
• Origin of Metals around Galaxies I: Catalogs of Metal-line Absorption Doublets from High-Resolution Quasar Spectra