Abstract
In the near future, new instruments will enable us to advance our knowledge of the reionization epoch. In optics and infrared, the new JWST space telescope will make it possible to detect primordial galaxies, the source of reionization. SPICA (the Japanese satellite on which Europe and France collaborated), in far-infrared, and ALMA, in millimetre-wave, will enable the detection of the most obscured galaxies, and those that form the most stars. Finally, in decimetric and metric waves, it will be possible to detect the atomic gas of the intergalactic medium, by intensity maps, with LOFAR (Low Frequency Array) and NenuFAR (New Extension in Nançay Upgrading LOFAR) and in the future SKA (Square Kilometer Array). Numerical simulations, taking into account the particularities of the first galaxies, which are very rich in gas and low in metals, predict that the galaxies detected by JWST will produce 40 % to 80 % of the reionization. Ionizing photon production increases with stellar mass (both star formation and AGN). Star formation dominates reionization over AGN at all redshifts. JWST could also detect explosions of Pop III starsinto pair-producingsupernovae. Gravitational lenses will be used to observe 15 to 20 of these behind galaxy clusters at z greater than 5. These supernovae may last 1 year, instead of 2-3 months for ordinarysupernovae. SKA precursors and scouts are already trying to detect the reionization signal : LOFAR, NenuFAR, MWA, Hera. SKA will not be operational until 2028. A redefinition of the budget took place in 2017 (over one billion euros). In a first stage, with a budget of half that, SKA1 will first be built, with SKAO, the organization of the 13 member countries (Australia, Canada, China, France, Germany, India, Italy, New Zealand, South Africa, Spain, Sweden, Netherlands, United Kingdom) representing 40 % of the world's population ! SKA1 consists of a low-frequency part, 130 000 dipoles in 512 arrays of 256 stations on the Boolardy site in Western Australia, and a medium-frequency part, 133 antennas of 15 m, plus 64 antennas of 13.5 m(MeerKAT) on the Karoo site in South Africa. The very wide-field instrument will be able to observe billions of galaxies, study BAOs, matter and dark energy, as well as reionization.
