Statistics of the epoch of reionization (EoR) 21-cm signal - II. The evolution of the power-spectrum error-covariance
Abstract
The epoch of reionization (EoR) 21-cm signal is expected to become highly non-Gaussian as reionization progresses. This severely affects the error-covariance of the EoR 21-cm power spectrum that is important for predicting the prospects of a detection with ongoing and future experiments. Most earlier works have assumed that the EoR 21-cm signal is a Gaussian random field where (1) the error-variance depends only on the power spectrum and the number of Fourier modes in the particular k bin, and (2) the errors in the different k bins are uncorrelated. Here, we use an ensemble of simulated 21-cm maps to analyse the error-covariance at various stages of reionization. We find that even at the very early stages of reionization (bar{x}_{H I}∼ 0.9), the error-variance significantly exceeds the Gaussian predictions at small length-scales (k > 0.5 Mpc-1) while they are consistent at larger scales. The errors in most k bins (both large and small scales) are however found to be correlated. Considering the later stages (bar{x}_{H I}=0.15), the error-variance shows an excess in all k bins within k ≥ 0.1 Mpc-1, and it is around 200 times larger than the Gaussian prediction at k ∼ 1 Mpc-1. The errors in the different k bins are all also highly correlated, barring the two smallest k bins that are anti-correlated with the other bins. Our results imply that the predictions for different 21-cm experiments based on the Gaussian assumption underestimate the errors, and it is necessary to incorporate the non-Gaussianity for more realistic predictions.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2017
- DOI:
- 10.1093/mnras/stw2599
- arXiv:
- arXiv:1606.03874
- Bibcode:
- 2017MNRAS.464.2992M
- Keywords:
-
- methods: statistical;
- cosmology: theory;
- dark ages;
- reionization;
- first stars;
- diffuse radiation;
- large-scale structure of Universe;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Published in Monthly Notices of the Royal Astronomical Society (MNRAS). Available at "this URL http://dx.doi.org/10.1093/mnras/stw2599"