Large-scale 3D mapping of the intergalactic medium using the Lyman Alpha Forest

TL;DR

This paper demonstrates that large-scale three-dimensional maps of the intergalactic medium at redshifts 2-4 can be accurately reconstructed from Lyman-alpha forest spectra using Wiener interpolation, matching the true structure on scales >30 h^-1 Mpc.

Contribution

It applies and validates the Wiener interpolation method to reconstruct 3D IGM maps from simulated Lyman-alpha spectra, showing high accuracy for current and future surveys.

Findings

Reconstructed maps have correlation coefficient r > 0.9 on scales >30 h^-1 Mpc.

Maps accurately recover large-scale statistical properties of the IGM.

Method is robust to variations in the covariance matrix used.

Abstract

Maps of the large-scale structure of the Universe at redshifts 2-4 can be made with the Lyman-alpha forest which are complementary to low redshift galaxy surveys. We apply the Wiener interpolation method of Caucci et al. to construct three-dimensional maps from sets of Lyman-alpha forest spectra taken from cosmological hydrodynamic simulations. We mimic some current and future quasar redshift surveys (BOSS, eBOSS and MS-DESI) by choosing similar sightline densities. We use these appropriate subsets of the Lyman-alpha absorption sightlines to reconstruct the full three dimensional Lyman-alpha flux field and perform comparisons between the true and the reconstructed fields. We study global statistical properties of the intergalactic medium (IGM) maps with auto-correlation and cross-correlation analysis, slice plots, local peaks and point by point scatter. We find that both the density field and the statistical proper- ties of the IGM are recovered well enough that the resulting IGM maps can be meaningfully considered to represent large-scale maps of the Universe in agreement with Caucci et al., on larger scales and for sparser sightlines than had been tested previously. Quantitatively, for sightline parameters comparable to current and near future surveys the correlation coefficient between true and reconstructed fields is r > 0.9 on scales > 30 h^-1 Mpc. The properties of the maps are relatively insensitive to the precise form of the covariance matrix used. The final BOSS quasar Lyman-alpha forest sample will allow maps to be made with a resolution of ~ 30 h^-1 Mpc over a volume of ~ 15 h^-3 Gpc^3 between redshifts 1.9 and 2.3.