Abstract
The main questions in the reionization era concern the rate of star formation, and their contribution to reionization. What role do black holes and active cores play in reionization ? Stars would be efficient reionizers, if UV radiation could flow freely out of galaxies. But most of it is absorbed by the atoms of the galaxy itself. The escape factor is thus one of the most crucial unknown parameters. To form stars, what are the density and physical properties of the molecular gas : is it hot, turbulent, inefficient ? How quickly can the gas be renewed by accretion from cosmic filaments, or how quickly is it ejected by supernova explosions ? Finally, the low abundance of heavy elements (metals) in the primordial gas will give rise to super-massive stars that we don't know about today : the exceptional Population stars III (PopIII). Where to look for galaxies with very high redshift ? Absorption in front of quasars and the Gunn-Peterson effect is one method. Observation of these absorptions shows that the fluctuations are enormous. Reionization is by no means homogeneous. Some regions are already reionized at z = 8, while other lines of sight will wait until z = 5.
