Papers › A method to determine the evolution history of the mean neutral Hydrogen fraction
A method to determine the evolution history of the mean neutral Hydrogen fraction
Rajesh Mondal, Somnath Bharadwaj, Ilian T. Iliev, Kanan K. Datta, Suman Majumdar, Abinash K. Shaw, Anjan K. Sarkar
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The light-cone (LC) effect imprints the cosmological evolution of the redshifted 21-cm signal T_b (n̂, ν) along the frequency axis which is the line of sight (LoS) direction of an observer. The effect is particularly pronounced during the Epoch of Reionization (EoR) when the mean hydrogen neutral fraction x̅_(HI)(ν) falls rapidly as the universe evolves. The multi-frequency angular power spectrum (MAPS) 𝒞_ℓ(ν₁,ν₂) quantifies the entire second-order statistics of T_b (n̂, ν) considering both the systematic variation along ν due to the cosmological evolution and also the statistically homogeneous and isotropic fluctuations along all the three spatial directions encoded in n̂ and ν. Here we propose a simple model where the systematic frequency (ν₁,ν₂) dependence of 𝒞_ℓ(ν₁,ν₂) arises entirely due to the evolution of x̅_(HI)(ν). This provides a new method to observationally determine the reionization history. Considering a LC simulation of the EoR 21-cm signal, we use the diagonal elements ν₁=ν₂ of 𝒞_ℓ(ν₁,ν₂) to validate our model. We demonstrate that it is possible to recover the reionization history across the entire observational bandwidth provided we have the value x̅_(HI) at a single frequency as an external input.
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