Statistics of the epoch of reionization (EoR) 21cm signal  II. The evolution of the powerspectrum errorcovariance
Abstract
The epoch of reionization (EoR) 21cm signal is expected to become highly nonGaussian as reionization progresses. This severely affects the errorcovariance of the EoR 21cm 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 21cm signal is a Gaussian random field where (1) the errorvariance 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 21cm maps to analyse the errorcovariance at various stages of reionization. We find that even at the very early stages of reionization (bar{x}_{H I}∼ 0.9), the errorvariance significantly exceeds the Gaussian predictions at small lengthscales (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 errorvariance 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 anticorrelated with the other bins. Our results imply that the predictions for different 21cm experiments based on the Gaussian assumption underestimate the errors, and it is necessary to incorporate the nonGaussianity 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;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Published in Monthly Notices of the Royal Astronomical Society (MNRAS). Available at "this URL http://dx.doi.org/10.1093/mnras/stw2599"