Impact of non-Gaussianity on reionization observations using SKA-Low

The Epoch of Reionization (EoR) is a part of the cosmic history when the universe changed its state from being completely neutral to completely ionized. The redshifted 21-cm radiation, originating from the neutral hydrogen (HI) in the inter-galactic medium (IGM), is a direct promising probe to this epoch. The major goal of several ongoing and upcoming EoR radio-interferometers is to measure the power spectrum (PS) of EoR 21-cm signal. An accurate measurement of the EoR 21-cm PS can potentially answer several questions related to the formation and the behaviour of the first luminous objects in our universe. This requires accurate error estimates of the 21-cm PS.
Several previous works, which constrained the reionization model parameters using the 21-cm PS, have used the PS error estimates assuming the signal to be a Gaussian random field. However, simulations show the EoR 21-cm signal to be inherently non-Gaussian whereby the error covariance of the 21-cm PS contains a trispectrum contribution that would be absent if the signal were Gaussian. Using the binned PS and trispectrum from simulations, here we present a methodology for incorporating these with the baseline distribution, system noise and foregrounds to make error predictions for observations with any radio-interferometric array. Here we present results considering the future SKA-Low observations only. Non Gaussianity enhances the errors in 21-cm PS by introducing a positive deviation relative to the Gaussian predictions. It also introduces correlations between the 21-cm PS errors in different k bins which can affect the parameter estimations. The non-Gaussianity increases errors in the inferred model parameters and also changes the correlations between them. The impact of non-Gaussianity increases with observation time and approaches towards the cosmic variance limit. We finally found that the non-Gaussian effects remain considerable during the later stages of reionization for SKA like instruments.