Probing the epoch of reionization using line-intensity mapping

Abstract

The epoch of reionization (EoR) is the period in the evolutionary history of the Universe when the first luminous sources were formed and emitted Lyman continuum photons capable of ionizing the neutral hydrogen in the intergalactic medium (IGM). This epoch marked an important episode in the cosmic timeline and was also the last major phase transition in the Universe. The earliest probes of this epoch include the optical depth measurement of Thomson scattering of the cosmic microwave background (CMB) photons, which can constrain the mid-point of the cosmic reionization. On the other hand, observations of the quasar spectra from high redshifts suggest that reionization might have ended around a redshift of 6. However, these limited observations do not give a comprehensive picture of the reionization era, such as the nature of the ionizing sources and how the reionization process progressed. The galaxy surveys with ALMA and JWST are probing this mysterious era by detecting a limited number of galaxy samples from the EoR and helping to uncover their nature. The key drawback of these instruments is that surveying large cosmological volumes is expensive and can only provide detections of early galaxies within a small field of view. Therefore, these surveys are not suitable for comprehending the EoR alone.