Recent deep observations of the young Universe (z > 4) by the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that normal star forming galaxies already show a non negligible amount of dust in their interstellar medium, which is supposed to significantly obscure the UV light emitted by their young stars and to affect their observed colours. As this sample will certainly increase with the next generation of high-redshift surveys, robust theoretical models will become crucial to interpret the impact of dusty galaxies on the early phases of star formation and on the reionization and thermal history of the intergalactic medium. Our research aims to address the following three key questions:
(i) Understand how dust is produced at cosmic dawn by the first generation of stars (Population III) and its role in driving the transition between massive Population III and Population II stars, with masses comparable to the ones observed in the Local Universe.
(ii) Elucidate the effect of dust on the rest-frame UV emission of the first galaxies, upon which most of their physical properties are derived.
(iii) Estimate the fraction of dust-obscured galaxies and evaluate their role in the metal enrichment and reionization of the intergalactic medium.
In the last years we developed a unique combination of theoretical models exploring dust nucleation in supernova ejecta as well as numerical simulations of young dusty galaxies constrained by presently available ALMA and Hubble Space Telescope observations. We constantly upgrade our models by improving their physics, to make them ready for the next fresh data provided by new large surveys planned with ALMA and by the forthcoming launch of the James Webb Space Telescope. The funding requested by our team will principally allow the dissemination of our results by supporting exchange activities with external collaborators, and the participation to international conferences and European meetings.
The proposed research relies on a unique combination of theoretical models, numerical simulations and detailed comparison with observational data. We will be able to assess the nature of the first dust producers by coupling for the first time detailed theoretical stellar 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 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. By using dustyGADGET we will be able to explore how dust properties and spatial distribution relative to the stars affect the rest-frame UV colours of the first galaxies and hence our ability to estimate their physical properties using current HST data and future JWST data. Finally, the combination between dustyGadget and radiative transfer simulations will provide a unique strategy to test the interplay between radiative and chemical feedback across cosmic scales by connecting the properties on galactic (interstellar medium) scales to the large scale intergalactic medium.
Before concluding, it is important to mention that the knowledge of the mass distribution and metallicity of stellar populations at high redshifts is of paramount importance for a number of reasons, that go well beyond the primary goals of the currently proposed research. One example is the expected mass distribution of their black hole remnants (Marassi et al. 2019a). It is well known that most of the black hole masses measured by the LIGO/VIRGO collaborations in their first and second observing runs require that these systems must have formed in low-metallicity environments. Understanding the nature of stellar populations at low metallicity, their mass distribution and formation rate is crucial to estimate the luminosity and detection rate of future binary black hole mergers, and their formation and coalescence sites (Schneider et al. 2017, Marassi et al. 2019b).