HIR4: cosmology from a simulated neutral hydrogen full sky using Horizon Run 4

TL;DR

This paper simulates future neutral hydrogen surveys using the Horizon Run 4 data, evaluating foreground removal methods and analyzing the impact of noise and instrument resolution on cosmological parameter recovery.

Contribution

It introduces realistic full-sky HI intensity maps from HR4, tests foreground removal techniques, and assesses their effectiveness in recovering cosmological parameters under realistic survey conditions.

Findings

Foreground removal methods can recover the cosmological power spectrum in ideal conditions.

Survey noise and beam size significantly affect the accuracy of cosmological parameter estimation.

Power loss on large scales can be corrected, but noise limits parameter recovery in realistic scenarios.

Abstract

The distribution of cosmological neutral hydrogen will provide a new window into the large-scale structure of the Universe with the next generation of radio telescopes and surveys. The observation of this material, through 21cm line emission, will be confused by foreground emission in the same frequencies. Even after these foregrounds are removed, the reconstructed map may not exactly match the original cosmological signal, which will introduce systematic errors and offset into the measured correlations. In this paper, we simulate future surveys of neutral hydrogen using the Horizon Run 4 (HR4) cosmological N-body simulation. We generate HI intensity maps from the HR4 halo catalogue, and combine with foreground radio emission maps from the Global Sky Model, to create accurate simulations over the entire sky. We simulate the HI sky for the frequency range 700-800 MHz, matching the sensitivity of the Tianlai pathfinder. We test the accuracy of the fastICA, PCA and log-polynomial fitting foreground removal methods to recover the input cosmological angular power spectrum and measure the parameters. We show the effect of survey noise levels and beam sizes on the recovered the cosmological constraints. We find that while the reconstruction removes power from the cosmological 21cm distribution on large-scales, we can correct for this and recover the input parameters in the noise-free case. However, the effect of noise and beam size of the Tianlai pathfinder prevents accurate recovery of the cosmological parameters when using only intensity mapping information.