Fast, large-volume, GPU-enabled simulations for the Ly forest: power spectrum forecasts for baryon acoustic oscillation experiments

Abstract

High-redshift measurements of the baryonic acoustic oscillation (BAO) scale from large Lyα forest surveys represent the next frontier of dark energy studies. As part of this effort, efficient simulations of the BAO signature from the Lyα forest will be required. We construct a model for producing fast, large-volume simulations of the Lyα forest for this purpose. Utilizing a calibrated semi-analytic approach, we are able to run very large simulations in 1 Gpc3 volumes which fully resolve the Jeans scale in less than a day on a desktop PC using a graphics processing unit enabled version of our code. The Lyα forest spectra extracted from our semi-analytical simulations are in excellent agreement with those obtained from a fully hydrodynamical reference simulation. Furthermore, we find that our simulated data are in broad agreement with observational measurements of the flux probability distribution and 1D flux power spectrum. We are able to correctly recover the input BAO scale from the 3D Lyα flux power spectrum measured from our simulated data, and estimate that a Baryon Oscillation Spectroscopic Survey like 104 deg2 survey with ∼15 background sources per square degree and a signal-to-noise ratio of ∼5 per pixel should achieve a measurement of the BAO scale to within ∼1.4 per cent. We also use our simulations to provide simple power-law expressions for estimating the fractional error on the BAO scale on varying the signal-to-noise ratio and the number density of background sources. The speed and flexibility of our approach is well suited for exploring parameter space and the impact of observational and astrophysical systematics on the recovery of the BAO signature from forthcoming large-scale spectroscopic surveys.