Rajesh Mondal

The effect of non-Gaussianity on error predictions for the Epoch of Reionization (EoR) 21-cm power spectrum

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 = root N-k for a Gaussian random field where N-k 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 N-k is increased. The value of [SNR](l) falls as reionization proceeds, dropping from similar to 500 at (x) over bar}(H1) = 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) proportional to root V if the volume is increased. For SNR << [SNR](l) we find SNR = root N-k/A with A similar to 0.95-1.75, 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 21-cm power spectrum, which till date have been largely based on the Gaussian assumption.

The effects of the small-scale DM power on the cosmological neutral hydrogen (HI) distribution at high redshifts

The particle nature of dark matter remains a mystery. In this paper, we consider two dark matter models---Late Forming Dark Matter (LFDM) and Ultra-Light Axion (ULA) models---where the matter power spectra show novel effects on small scales. The high redshift universe offers a powerful probe of their parameters. In particular, we study two cosmological observables: the neutral hydrogen (HI) redshifted 21-cm signal from the epoch of reionization, and the evolution of the collapsed fraction of HI in the redshift range

Statistics of the epoch of reionization 21-cm signal – I. Power spectrum error-covariance

2 < z < 5

Towards simulating and quantifying the light-cone EoR 21-cm signal

. We model the theoretical predictions of the models using CDM-like N-body simulations with modified initial conditions, and generate reionization fields using an excursion-set model. The N-body approximation is valid on the length and halo mass scales studied. We show that LFDM and ULA models predict an increase in the HI power spectrum from the epoch of reionization by a factor between 2--10 for a range of scales

Statistics of the epoch of reionization (EoR) 21-cm signal – II. The evolution of the power-spectrum error-covariance

0.1 4 \times 10^5

Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum

(for LFDM) and the axion mass

The shape and size distribution of H ii regions near the percolation transition

m_a > 2.6 \times 10^{-23} \, \rm eV

Line-of-Sight Anisotropies in the Cosmic Dawn and Epoch of Reionization 21-cm Power Spectrum

(for ULA). The comparison of the collapsed mass fraction inferred from damped Lyman-

Modelling the 21-cm Signal from the Epoch of Reionization and Cosmic Dawn

\alpha

A fast estimator for the bispectrum and beyond - a practical method for measuring non-Gaussianity in 21-cm maps

observations to the theoretical predictions of our models lead to the weaker bounds: