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

Abstract

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 realisation 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 $\Delta ^2_{21}=10~\mathrm{mK}^2$ 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 hours, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data.

Studying the multifrequency angular power spectrum of the cosmic dawn 21-cm signal

“…Ba ˜ nados et al 2018 ;Davies et al 2018 ;Ďuro v č íko v á et al 2020 ;Reiman et al 2020 ;Wang et al 2020 ;Yang et al 2020 ;Greig et al 2022 ), Lyman break galaxies (Mason et al 2018 ;Hoag et al 2019 ;Naidu et al 2020 ), the measurements of the ef fecti ve optical depth of the Ly-α (and Ly-β) forests (e.g. McGreer, Mesinger & D'Odorico 2014 ;Kulkarni et al 2019 ;Raste et al 2021 ;Zhu et al 2021Zhu et al , 2022, and the high-z Ly-α emitters clustering measurements (e.g. Faisst et al 2014 ;Sobacchi & Mesinger 2015 ;Santos, Sobral & Matthee 2016 ;Wold et al 2022 ) have put some lose bounds on the average H I fraction in the IGM.…”