The roughly equal brightness of the cosmic infrared and optical backgrounds informs us that half the light from the formation and evolution of galaxies is obscured by dust. However, while surveys at rest-frame UV wavelengths have mapped out the history of un-obscured star formation from the present day back to z ~ 8 and above, beyond z = 3 our census of the dust-obscured, and hence of the total star formation activity is severely incomplete. The main goals of this research proposals are to: (i) understand the nature of the sources of dust in early Universe; (ii) elucidate the key properties of galaxies that determine the dust content in their interstellar medium (ISM); (iii) assess the amount of dust-obscured star formation in the high redshift Universe and the consequences that this has on the process of cosmic reionization. We plan to address these important goals through a combination of theoretical models, numerical simulations and comparison with data taken from the most advanced facilities that are currently working (ALMA) or that will be soon available (JWST and MUSCAT on LMT). By funding a dedicated team of young and experienced researchers, supporting exchange visits with external collaborators and the dissemination of project results, the proposed project holds the promise for a significant advancement in our exploration of the dusty Universe at the cosmic dawn.
The proposed research relies on a combination of theoretical models, numerical simulations and detailed comparison with observational data.
To advance our understanding of the role of stellar dust enrichment, we need to: (i) reduce the uncertainties on the dust destruction efficiency by the SN reverse shock; (ii) have a better understanding of how the dust properties (composition and size distribution) produced in SN ejecta depends on the properties of the progenitor stars and of the SN explosion (energies, rotation, metallicity); (iii) improve and test the mass loss prescriptions of AGB stars, to better constrain how their dust yields depend on metallicity and stellar mass. On the other side, grain growth in dense molecular clouds may be problematic because of the presence of icy mantles (Ferrara et al. 2016; Ceccarelli et al. 2018). An alternative possibility is that grain growth occurs in the cold neutral medium, that is characterized by lower densities and higher temperatures (Zhukowska et al. 2018). While this appears to be a promising environment for grain growth in Milky Way-like conditions, the cold neutral medium of high redshift galaxies may be characterized by very different conditions, with more intense and harder interstellar radiation fields, and larger mean densities. Hence, to fully assess the feasibility of grain growth in the ISM of high-z galaxies (iv) we need to explore the efficiency of this process in a large range of physical conditions. Finally, to predict the colors of high-z galaxies and their dependence on galaxy properties and redshift, (v) detailed numerical simulations have to be run, with a sufficient resolution to map the properties of the ISM and the variations of the dust-to-gas mass ratio in different ISM phases. A self consistent description of the stellar dust yields and of grain growth in the ISM of high redshift galaxies is required to exploit future data that will be soon obtained by the James Webb Space Telescope and by deep ALMA observations of high-z galaxy candidates.
A complementary facility for directly detecting dustin z > 4 galaxies is the 50m-diameter Large Millimeter Telescope Alfonso Serrano (LMT, Hughes et al. 2010). MUSCAT is a large-format photometer sensitive in a band centered at 1.1 mm. The camera will be commissioned in December 2018, and data will be available on the time scale of this project. The inherent measured biases in previous extragalactic observations are due to the limitations in the size of ground-based and space-borne mm-wavelength telescopes (e.g. Herschel), or the field-of-view of their instruments (e.g. ALMA). The angular resolution provided by the relatively small Herschel telescope (3.5m diameter, 18 arcsecond wide beam at 250µm) limited the accuracy of the source positions and source confusion made it difficult to detect normal and infrared luminous galaxies (10^12 Lsun luminosity limit) at high-redshifts. Of the 300,000 sources detected in the 550 deg2 Herschel-ATLAS (H-ATLAS) sub-mm survery with SPIRE, it has been possible to identify optical counterparts and reliable redshifts for only one third of the total, at z