The observed 21 cm signal from the epoch of reionization will be distorted along the line of sight by the peculiar velocities of matter particles. These redshift-space distortions will affect the contrast in the signal and will also make it anisotropic. This anisotropy contains information about the cross-correlation between the matter density field and the neutral hydrogen field, and could thus potentially be used to extract information about the sources of reionization. In this paper, we study a collection of simulated reionization scenarios assuming different models for the sources of reionization. We show that the 21 cm anisotropy is best measured by the quadrupole moment of the power spectrum. We find that, unless the properties of the reionization sources are extreme in some way, the quadrupole moment evolves very predictably as a function of global neutral fraction. This predictability implies that redshiftspace distortions are not a very sensitive tool for distinguishing between reionization sources. However, the quadrupole moment can be used as a model-independent probe for constraining the reionization history. We show that such measurements can be done to some extent by first-generation instruments such as LOFAR, while the SKA should be able to measure the reionization history using the quadrupole moment of the power spectrum to great accuracy.
Bibliographical noteFunding Information:
SM would like to thank Raghunath Ghara for useful discussions related to the effect of spin temperature fluctuations on the EoR 21 cm signal. The research described in this paper was supported by a grant from the Lennart and Alva Dahlmark Fund. GM is supported by Swedish Research Council project grant 2012-4144. The PRACE4LOFAR simulations were performed on the Curie system at TGCC under PRACE projects 2012061089 and 2014102339. This work was supported by the Science and Technology Facilities Council (grant no. ST/L000652/1). KKD would like to thank DST for support through the project SR/FTP/PS-119/2012 and the University Grant Commission (UGC), India for support through UGC-faculty recharge scheme (UGC-FRP) vide ref. no. F.4-5(137- FRP)/2014(BSR). VJ would like to thank the Netherlands Foundation for Scientific Research (NWO) for financial support through VENI grant 639.041.336. LVEK acknowledges the financial support from the European Research Council under ERC-StartingGrant FIRSTLIGHT - 258942.
© 2015 The Authors. Published by Oxford University Press.
- Dark ages, reionization, first stars
- Methods: numerical