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Observations of the neutral Hydrogen (HI ) 21-cm signal hold the potential of allowing us to map out the cosmological large scale structures (LSS) across the entire post-reionization era ($z leq 6$). Several experiments are planned to map the LSS over a large range of redshifts and angular scales, many of these targeting the Baryon Acoustic Oscillations. It is important to model the HI distribution in order to correctly predict the expected signal, and more so to correctly interpret the results after the signal is detected. In this paper we have carried out semi-numerical simulations to model the HI distribution and study the HI power spectrum $P_{HI}(k,z)$ across the redshift range $1 le z le 6$. We have modelled the HI bias as a complex quantity $tilde{b}(k,z)$ whose modulus squared $b^2(k,z)$ relates $P_{HI}(k,z)$ to the matter power spectrum $P(k,z)$, and whose real part $b_r(k,z)$ quantifies the cross-correlation between the HI and the matter distribution. We study the $z$ and $k$ dependence of the bias, and present polynomial fits which can be used to predict the bias across $0 le z le6$ and $0.01 le k le 10 , {rm Mpc}^{-1}$. We also present results for the stochasticity $r=b_r/b$ which is important for cross-correlation studies.
Measurements of the post-reionization 21-cm bispectrum $B_{{rm HI}}(mathbf{k_1},mathbf{k_2},mathbf{k_3})$ using various upcoming intensity mapping experiments hold the potential for determining the cosmological parameters at a high level of precision
The post-reionization ${rm HI}$ 21-cm signal is an excellent candidate for precision cosmology, this however requires accurate modelling of the expected signal. Sarkar et al. (2016) have simulated the real space ${rm HI}$ 21-cm signal, and have model
The neutral hydrogen (HI) and its 21 cm line are promising probes to the reionization process of the intergalactic medium (IGM). To use this probe effectively, it is imperative to have a good understanding on how the neutral hydrogen traces the under
The spatial distribution of neutral hydrogen (HI) in the Universe contains a wealth of cosmological information. The 21 cm emission line can be used to map the HI up to very high redshift and therefore reveal us something about the evolution of the l
The epoch of reionization is one of the least known chapters in the evolutionary history of the Universe. This thesis investigates two major approaches to unveil the reionization history of the Universe using HI 21-cm maps.The most discussed approach