| The 21cm Power Spectrum After Reionization (2008) | |||||||||
Abstract | |||||||||
| We discuss the 21cm power spectrum (PS) following the completion of reionization. In contrast to the reionization era, this PS is proportional to the PS of mass density fluctuations, with only a small modulation due to fluctuations in the ionization field on scales smaller than the mean-free-path of ionizing photons. We derive the form of this modulation, show that its effect on the observed 21cm PS is not degenerate with uncertainties in cosmological parameters, and demonstrate that its contribution can be measured by observations. In contrast to the 21cm PS observed prior to reionization, in which HII regions dominate the ionization structure, the simplicity of the 21cm PS after reionization will enhance its utility as a cosmological probe by removing the need to separate the PS into physical and astrophysical components. As a demonstration, we consider the Alcock-Paczynski test and show that the next generation of low-frequency arrays could measure the angular distortion of the PS at the percent level for z~3-5.. Comment: 10 pages, 5 figures. Submitted to MNRAS | |||||||||
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