Abstract

One of the key question of modern extragalactic astronomy is to determine when the first generation of stars and galaxies started to bathe the Universe in light. According to the most recent simulations, this “Cosmic Dawn” occurred _{200 Myr after the Big-Bang (corresponding to a redshift of z}20). The recent claim of the detection of a redshifted 21cm absorption in the CMB suggests that the formation of the first generation of stars and galaxies happened at z~17. However, observing these galaxies at very high-redshift (z>11) is well beyond the capabilities of current ground-based and space instruments. However recently high-redshift galaxies discovered at fascinating distances z>8, were interpreted in terms of ages and intense star formation histories. These galaxies are revealed mature with ages of 500 million years, starting just after the Big-Bang. Such early systems with significant stellar masses and star formation rates which decline with time are not easily reproduced by contemporary numerical simulations. The physics of these galaxies (mass growth, dissipation by ionizing energy, gas and electronic densities) are the main objectives, to be related to dark matter haloes and to the growth of supermassive black holes. In this talk I will review the latest results on the search for and study of the most distant sources, in terms of physical properties (age, SFR , stellar mass, dust mass) and on their contribution to the reionisation budget.