Abstract
The Epoch of Reionization (EoR) 21-cm signal is expected to become increasingly non-Gaussian as reionization proceeds. We have used seminumerical simulations to study how this affects the error predictions for the EoR 21-cm power spectrum. We expect SNR=√{N_k} for a Gaussian random field where Nk is the number of Fourier modes in each k bin. We find that non-Gaussianity is important at high SNR where it imposes an upper limit [SNR]l. For a fixed volume V, it is not possible to achieve SNR > [SNR]l even if Nk is increased. The value of [SNR]l falls as reionization proceeds, dropping from ˜500 at bar{x}_{H I} = 0.8-0.9 to ˜10 at bar{x}_{H I} = 0.15 for a [150.08 Mpc]3 simulation. We show that it is possible to interpret [SNR]l in terms of the trispectrum, and we expect [SNR]_l ∝ √{V} if the volume is increased. For SNR ≪ [SNR]l we find SNR= √{N_k}/A with A ˜ 0.95-1.75, roughly consistent with the Gaussian prediction. We present a fitting formula for the SNR as a function of Nk, with two parameters A and [SNR]l that have to be determined using simulations. Our results are relevant for predicting the sensitivity of different instruments to measure the EoR 21-cm power spectrum, which till date have been largely based on the Gaussian assumption.
Author
Mondal, Rajesh; Bharadwaj, Somnath; Majumdar, Suman; Bera, Apurba; Acharyya, Ayan
Journal
Monthly Notices of the Royal Astronomical Society: Letters,
Paper Publication Date
April 2015
Paper Type
Astrostatistics