Exploring the epoch of first light and the cosmic history of galaxies

Exploring the epoch of first light and the cosmic history of galaxies. The aim of my research proposal is to explore one of the key frontiers of modern science and address some of the most outstanding questions in extra-galactic astrophysics: when did the first galaxies form and how did they evolve to form the complexity and variety of systems we see around us today? Several pieces of evidence now suggest that the epoch of ``first light'', when the first galaxies formed, should have occurred just a few hundred million years after the initial Big Bang. This early epoch, when the first substantial systems of stars began to shine represents a key step in the history of the Universe, which shaped the entire evolutionary history of galaxies thereafter. However, despite dramatic technological advances in our ability to study distant galaxies, very little is currently known about these primeval epochs, and ``a single example of the first generation of galaxies is yet to be observed''. Therefore, many questions still need to be answered. When did the first star-formation begin and how rapid was it? Were these sources similar to the stars and galaxies we observe today? And how did the heating from these first sources affect the subsequent history of galaxy formation? The main reason for the lack of any direct information on this fundamental epoch is that these sources are completely invisible to classic optical telescopes. In fact, due to the expansion of the Universe, the optical/ultraviolet light from these extremely distant galaxies is shifted towards longer wavelengths and is detectable only in the infrared. Until now, deep astronomical observations in the near-infrared have been technologically challenging and limited to very small areas in the sky. This, combined with the rarity and faintness of the most distant galaxies, has made these sources extremely difficult to discover. However, new facilities on ground-based and space-borne telescopes, have recently facilitated a series of surveys which, over the next 3-5 years, promise to revolutionise our understanding of galaxy formation. Exploiting my key position in these new initiatives and building on my recent successful research, I will be able to explore the uncharted Universe at the epoch of the first galaxies. I will use these revolutionary new datasets to isolate several hundred primeval galaxies, obtaining accurate measurements of their distance and, more crucially, their masses, the rate at which they are forming stars and their age. This will provide the first direct census of the first and most distant galaxies in the Universe, giving fundamental insight into the physics of the first stars and providing invaluable constraints to the models of galaxy formation. In addition to the study of the young Universe described above, I will exploit the unique power of these new surveys to obtain a truly representative picture of the evolution of galaxies over all of cosmic time. In fact, tracing the assembly history of galaxies from the formation of the first stars, 13 billions years ago, through the entire history of the Universe remains a primary goal for observational and theoretical cosmology. In the nearby Universe we observe a large variety of galaxies, differing in size, morphology, stellar content, mass, environment etc. How did this heterogeneity come to be? Armed with a unique sample of half a million galaxies spanning 90\% of the history of the Universe I will be able to directly observe the building process of stars in the various type of galaxies (e.g. ellipticals, spirals, irregulars) as a function of cosmic time. It will be possible, for example, to understand why and when most of the massive galaxies ceased to form stars a long time ago, while other galaxies, like our own Milky Way, are still actively forming stars today.