The effect of nonGaussianity on error predictions for the Epoch of Reionization (EoR) 21cm power spectrum.
Abstract
The Epoch of Reionization (EoR) 21cm signal is expected to become increasingly nonGaussian as reionization proceeds. We have used seminumerical simulations to study how this affects the error predictions for the EoR 21cm power spectrum. We expect SNR=√{N_k} for a Gaussian random field where N_{k} is the number of Fourier modes in each k bin. We find that nonGaussianity 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 N_{k} is increased. The value of [SNR]_{l} falls as reionization proceeds, dropping from ∼500 at bar{x}_{H I} = 0.80.9 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 ∼ 0.951.75, roughly consistent with the Gaussian prediction. We present a fitting formula for the SNR as a function of N_{k}, 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 21cm power spectrum, which till date have been largely based on the Gaussian assumption.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2015
 DOI:
 10.1093/mnrasl/slv015
 arXiv:
 arXiv:1409.4420
 Bibcode:
 2015MNRAS.449L..41M
 Keywords:

 methods: statistical;
 cosmology: theory;
 dark ages;
 reionization;
 first stars;
 diffuse radiation;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Accepted for publication in MNRAS Letters. The definitive version is available at http://mnrasl.oxfordjournals.org/content/449/1/L41