Correlations in the three-dimensional Lyman-alpha forest contaminated by high column density absorbers

Abstract

Correlations measured in three dimensions in the Lyman-alpha forest are contaminated by the presence of the damping wings of high column density (HCD) absorbing systems of neutral hydrogen (HI; having column densities $N(\mathrm{HI})>1.6\times 10^{17}\mathrm{atoms}{\mathrm{cm}}^{-2}$), which extend significantly beyond the redshift-space location of the absorber. We measure this effect as a function of the column density of the HCD absorbers and redshift by measuring 3D flux power spectra in cosmological hydrodynamical simulations from the Illustris project. Survey pipelines exclude regions containing the largest damping wings. We find that, even after this procedure, there is a scale-dependent correction to the 3D Lyman-alpha forest flux power spectrum from residual contamination. We model this residual using a simple physical model of the HCD absorbers as linearly biased tracers of the matter density distribution, convolved with their Voigt profiles and integrated over the column density distribution function. We recommend the use of this model over existing models used in data analysis, which approximate the damping wings as top-hats and so miss shape information in the extended wings. The simple 'linear Voigt model' is statistically consistent with our simulation results for a mock residual contamination up to small scales ($|k|<1h{\mathrm{Mpc}}^{-1}$). It does not account for the effect of the highest column density absorbers on the smallest scales (e.g., $|k|>0.4h{\mathrm{Mpc}}^{-1}$ for small damped Lyman-alpha absorbers; HCD absorbers with $N(\mathrm{HI})\sim 10^{21}\mathrm{atoms}{\mathrm{cm}}^{-2}$). However, these systems are in any case preferentially removed from survey data. Our model is appropriate for an accurate analysis of the baryon acoustic oscillations feature. It is additionally essential for reconstructing the full shape of the 3D flux power spectrum.

13 pages, 11 figures. Minor changes to match version published in MNRAS

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• Baryon acoustic oscillations at z = 2.34 from the correlations of Ly$\alpha$ absorption in eBOSS DR14
• The Abell 3391/95 galaxy cluster system: A 15 Mpc intergalactic medium emission filament, a warm gas bridge, infalling matter clumps, and (re-) accelerated plasma discovered by combining SRG/eROSITA data with ASKAP/EMU and DECam data
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• Cosmology beyond BAO from the 3D distribution of the Lyman-$\alpha$ forest
• Constraints on the cosmic expansion rate at redshift 2.3 from the Lyman-$\alpha$ forest
• $5\sigma$ tension between Planck cosmic microwave background and eBOSS Lyman-alpha forest and constraints on physics beyond $\Lambda$CDM
• Damped Lyman-alpha Absorbers from Sloan Digital Sky Survey DR16Q with Gaussian processes
• The 3D Lyman-$\alpha$ Forest Power Spectrum from eBOSS DR16
• Massive neutrinos and degeneracies in Lyman-alpha forest simulations
• The Alcock-Paczyński effect from Lyman-$\alpha$ forest correlations: Analysis validation with synthetic data
• Imprints of the first billion years: Lyman limit systems at $z\sim 5$
• Bayesian methods for fitting Baryon Acoustic Oscillations in the Lyman-$\alpha$ forest
• The cross-correlation of galaxies in absorption with the Lyman $\alpha$ forest
• Measurement of the small-scale 3D Lyman-$\alpha$ forest power spectrum
• Boosting Line Intensity Map Signal-to-Noise with the Ly-$\alpha$ Forest Cross-Correlation
• An Analytically Tractable Marked Power Spectrum
• 3D Correlations in the Lyman-$\alpha$ Forest from Early DESI Data
• Mock data sets for the Eboss and DESI Lyman-$\alpha$ forest surveys