Early on, the Universe consisted of a near-uniform mixture of hydrogen, helium, dark matter and radiation. The emergence of structure from a stochastic background of fluctuations in the period between 400,000 years and 1 billion years after the Big Bang is the main subject of this proposal. This transition from the "dark ages" in the history of the Universe to "cosmic dawn" saw the formation of the first autonomous sources of radiation, stars and black holes. This "renaissance" of light led to the heating and reionization of the intergalactic medium. The first supernova explosions start the process of metal and dust enrichment, releasing in their surroundings elements heavier than helium and dust grains condensed in their expanding ejecta. Despite the amount of new data rapidly accumulating on the primeval Universe, the transition from the dark ages to cosmic dawn and the physical properties of the sources responsible for the reionization of the intergalactic medium still remain largely unconstrained.
Our research aims to address the following three key questions:
(i) What is the nature of the first stars to shine through the Universe?
(ii) What is the best observational strategy to observe the first stars?
(iii) What was the contribution of the first stars to cosmic reionization?
In the last years we developed a unique combination of theoretical models exploring the Universe at cosmic dawn with semi-analytical models and cosmological hydro-dynamical simulations. We constantly upgrade our models by improving their physics, to make them ready for the next fresh data provided by new surveys planned with new observational facilities, such as the James Webb Space Telescope and the European Extremely Large Telescope. The funding requested by our team will principally allow the acquisition of small computational facilities, the support of exchange activities with external collaborators, and payment of publication fees.
The proposed research relies on a unique combination of theoretical models, numerical simulations and detailed comparison with observational data. We will explore the nature of the first stars, black hole seeds and the properties of the first galaxies by coupling for the first time detailed theoretical stellar metal and dust yields with cosmological simulations where star formation and dust enrichment are treated self-consistently. This approach has never been attempted before.
By running simulations on different cosmological scales, we will follow the environmental dependent Population III/Population II transition, allowing us to assess the role played by dust grains and gas-phase metals in setting the nature of the stellar populations that inhabit the first galaxies. This, in turn, will allow us to estimate the role of the first galaxies in the first phase of cosmic reionization and metal enrichment as the efficiency of ionizing photons production and rate of supernova explosions strongly depend on the stellar mass and metallicity.
In addition, metal and dust pollution of the interstellar medium of the first galaxies have a dramatic effect on their observable properties. The combination between dustyGadget and radiative transfer simulations with publicly available codes such as CLOUDY and SKIRT will allow us to make detailed predictions on the detectability of Pop III stars and their host galaxies with future and proposed observational facilities.
Finally, these small-scale simulations will be complemented by CAT to connect the properties of star forming regions at cosmic dawn with the mature galaxy and AGN populations that we observe at 4