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Implications of the z > 5 Lyman-α forest for the 21-cm power spectrum from the epoch of reionization

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Raste, Janakee 
Kulkarni, Girish 
Keating, Laura C 
Haehnelt, Martin G 
Chardin, Jonathan 


Our understanding of the intergalactic medium at redshifts z = 5–6 has improved considerably in the last few years due to the discovery of quasars with z > 6 that enable Lyman-α forest studies at these redshifts. A realization from this has been that hydrogen reionization could end much later than previously thought, so that large ‘islands’ of cold, neutral hydrogen could exist in the IGM at redshifts z = 5–6. By using radiative transfer simulations of the IGM, we consider the implications of the presence of these neutral hydrogen islands for the 21-cm power spectrum signal and its potential detection by experiments such as HERA, SKA, LOFAR, and MWA. In contrast with previous models of the 21-cm signal, we find that thanks to the late end of reionization the 21-cm power in our simulation continues to be as high as Δ212 = 10 mK2 at k ∼ 0.1 h cMpc−1 at z = 5–6. This value of the power spectrum is several orders of magnitude higher than that in conventional models considered in the literature for these redshifts. Such high values of the 21-cm power spectrum should be detectable by HERA and SKA1-low in ∼1000 h, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data.



intergalactic medium, cosmology: theory, dark ages, reionization, first stars

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Monthly Notices of the Royal Astronomical Society

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Royal Astronomical Society


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Science and Technology Facilities Council (ST/S000623/1)
Engineering and Physical Sciences Research Council (EP/P020259/1)
Science and Technology Facilities Council (ST/M007065/1)
STFC (ST/M007073/1)