Abstract

In this talk I will review the recent advance in our understanding of the reionization period of the Universe. The reionization period of hydrogen is a key phase transition in the history of the Universe that took place between about 200 millions years and one Giga-year after the Big-Bang. This transition originates fron the formation of the first luminous sources that emit UV photons capable of ionizing the hydrogen atoms residing in the intergalactic medium. The transition is spread in time and complete when the different ionized regions (HII regions) in expansion eventually overlap, leading to a Universe that is completely ionized. This transition is very important for our understanding of the galaxy formation mechanism in the early Universe and to explain the morphology of the galaxies we see today. The observation of this transition are still poorly constrained but a range of new campaigns are going to be undertaken to characterize this epoch in details in the next decade. In the meantime a lot of effort are deployed to perform numerical simulations of this transition in order to prepare our understanding of the future observations. In this talk, I will discuss the different observational probes and simulation techniques that would help us to have a better understanding of the period of reionization in the near future.

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