Suman Majumdar, Somnath Bharadwaj, T. Roy Choudhury
We have used semi-numerical simulations of reionization to study the behaviour of the power spectrum of the EoR 21-cm signal in both real and redshift space. We have considered two models of reionization, one which has homogeneous recombination (HR) and the other incorporating inhomogeneous recombination (IR). Considering the large scales first, we find that the predictions of these two models are similar. Both the real space HI power spectrum P^r(k) and the monopole moment of the redshift space HI power spectrum P^s_0(k), fall sharply to a minima as the neutral fraction declines from x_{HI} =1 to 0.8 in the early stages of reionization. As reionization proceeds, P^r and P^s_0 subsequently rise to a maxima at x_{HI} ~ 0.4-0.5, and then declines in the later stages of reionization. In the early stages of reionization (x_{HI} >= 0.8) the quadrupole moment of the HI power spectrum has a value consistent with P^s_2 /P^s_0=50/49 predicted by the linear theory of redshift space distortion. This ratio falls abruptly at x_{HI} = 0.7, and is negative with P^s_2 /P^s_0 ~ (-0.5) through the subsequent stages of reionization. The predictions of the HR and IR models, we find, differ at small and intermediate length-scales. It is possible to qualitatively interpret the results of the simulations in terms of the fluctuations in the matter distribution and the fluctuations in the neutral fraction which have power spectra and dimensionless cross-correlation P_{\Delta \Delta}(k), P_{xx}(k) and R=P_{\Delta x}/\sqrt{P_{\Delta \Delta} P_{xx}} respectively. We find R=-1 at large scales through all stages of reionization. This provides a simple picture where we are able to qualitatively interpret the behaviour of both the real space and redshift space power spectra at large scales with varying x_{HI} entirely in terms of a just two quantities, namely x_{HI} and the ratio P_{xx}/P_{\Delta \Delta}.
View original:
http://arxiv.org/abs/1209.4762
No comments:
Post a Comment