Final Report Summary - COSMIC_DAWN (Cosmic Dawn – The Emergence of Black Holes and Galaxies in the Universe)
This ERC program resulted in a number of significant achievements over the funding period (2012-2017). One specific objective was to find a significant number of previously unknown quasars (actively accreting supermassive black holes) at the highest possible redshifts. The quasar search conducted as part of this ERC program resulted in more than doubling the known quasar population in the first Gyr of the Universe, and laid the foundation to finding the highest-redshift quasar known to data (at z=7.5). Besides these discoveries, major effort was put into characterizing the quasars, their host galaxies, and their cosmic environment, using multi-wavelength follow-up observations. These studies have shown that the quasars host supermassive black holes, often exceeding 1 billion solar masses, out to the very highest redshifts accessible. These quasar hosts contain significant concentrated (~kpc-scale) amounts of gas and dust that are enriched by heavy metals. ALMA measurements have also identified the presence of close companions to some of the most distant quasars, including one quasar that is apparently merging with another galaxy. All these findings put challenging constraints on the models of black hole growth and galaxy formation in the first Gyr of the Universe. Another aspect of the project was to derive an unbiased census of molecular gas in the early universe, i.e. to constrain the cosmic evolution of molecular gas as a function of lookback time, through a novel observational technique (molecular frequency scans of cosmological deep fields). Similar studies are routine for deriving the cosmic star formation rate density, but have not been done for the molecular gas before. First results from this initiative indicate a significant increase of the cosmic molecular gas density from redshift 0 to ~1.5 (when the universe was ~half of its current age), similar to what is seen in the cosmic star formation rate density. Overall, this ERC proposal greatly increased our understanding of the physical properties of the earliest massive objects in the universe, and shed first light on the evolution of the cosmic molecular gas density in galaxies after the universe emerged from the cosmic ‘dark ages’.