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The first protoclusters of galaxies: probes of star formation in the infancy of the Universe

Final Report Summary - FIRSTGAL (The first protoclusters of galaxies: probes of star formation in the infancy of the Universe)

The main focus of the project has been the study of galaxy formation and evolution within the first billion years after the Big Bang, primarily using Hubble Space Telescope data, and related modeling to understand how the early objects subsequently evolve into the galaxies and galaxy clusters observed in the local universe. The initial stage has been very successful in both the observational and modeling aspects, leading to a total of 22 submitted and refereed publications by the Fellow. In particular the project provided the best characterization of the properties of bright galaxies at redshift z~8, which are objects observed when the Universe was just about 650 Million years old (more than 13 billion years ago). In addition, the project studied the clustering properties of galaxies at redshift z>7 for the first time. The clustering measurement is very important because it provides, at least in the statistical sense, the total weight of a galaxy (stars plus dark matter). This measurement allowed the Fellow and his team to demonstrate that galaxies as bright as our own Milky Way were already present at those early times, but had stellar and dark-matter halo masses about ten times smaller. This result derives from the fact that the stars in those galaxies are younger and hotter, and therefore brighter per unit mass at the wavelengths observed by Hubble, compared to the old stellar population of our own galaxy. In addition, the Fellow modeled (1) the connection between assembly of galaxies and of their dark-matter halos; (2) the link between star formation and Gamma Ray Burst explosions; and (3) the evolution of dense stellar systems using sophisticated computer simulations. Overall, these activities contributed to the advancement of the state of the art of galaxy formation and evolution, and provided new clues to address one of the most fundamental questions of astronomy: "Where do we come from?". An early termination of the project after about 18 months has been triggered by the relocation of the Fellow to The University of Melbourne, Australia where he joined the School of Physics as faculty member. The Fellow started there a new research group and the later stages of the project discussed in the proposal are now continuing to be carried out through support from the Australian Research Council. Further information on the Hubble Space Telescope observations can be found on the website of the Brightest of Reionizing Galaxies (BoRG) survey, led by the Fellow: http://borg.physics.ucsb.edu/. The website has links to astronomical data images released to the public, both for outreach and for exploitation by other scientists. Overall, the project strengthened existing international collaborations between Europe and the United States, and led to the establishment of new ones, in particular within Europe (UK-Spain) and with Australia.