The haloes that reionized the Universe

We study the reionization of the Universe due to haloes that host galaxies undergoing bursts of star formation. By comparing the recent results from the James Webb Space Telescope (JWST) with the cosmological hydrodynamical simulation eagle at z ≥ 6, we find that bursty galaxies have specific star formation rate, sSFR > 10-2 Myr-1, and magnitude, MUV ≤ -17. Most of them reside in haloes of mass ∼ 109 M⊙ and some in more massive haloes. We then construct the models of escape fraction and find that a skewed Gaussian function with a flat tail towards the high mass end best describes the mean dependence of escape fraction on halo mass, considering the haloes hosting bursty galaxies as the primary drivers of reionization. We implement the models of escape fraction in the code 21cmfast to study the progress of reionization and derive the evolution of the mean ionized fraction that agrees well with observations. We also calculate the brightness temperature, spin temperature, and kinetic temperature and further study the spatial fluctuations in these quantities to gain insights into the progress of reionization. We compute the 21 cm power spectrum and predict a peak in power at 180 MHz corresponding to redshift, z ≈ 6.8, that is testable by the upcoming Square Kilometre Array (SKA). Our findings suggest that the Universe was reionized by the haloes of ≳ 109 M⊙.