New advances in the derivation of the physical parameters of distant galaxies with MIRI/JWST photometry

The large amount of data provided by the James Webb Space Telescope (JWST) in the first three years of scientific mission unveiled a great number of high-redshift galaxies. This was possible thanks to the incomparable sensitivity of JWST imaging and spectroscopy, which allows us to probe optical rest-frame emission lines, stellar masses, and star formation histories of galaxies at Cosmic Dawn. In this work, I extended the ASTRODEEP catalogue to longer wavelengths by including imaging data from the Mid Infrared Instrument (MIRI) of the James Webb Space Telescope. I performed aperture and template-fitting photometry using state-of-the-art codes to obtain fluxes of 36730 galaxies in the GOODS-South field and then, by fitting the observed Spectral Energy Distributions (SED), I retrieved the physical parameters, most importantly the stellar mass, of 2959 sources. MIRI photometry is fundamental for better constraining such parameter because it probes the rest-frame Near Infrared emission of galaxies from z > 3, where old and low-mass stars, which make up the bulk of the mass budget, emit. Obtaining a correct estimate of galaxies stellar masses at Cosmic Dawn is significant in understanding the formation of galaxies by means of the amount of stars formed. Moreover, improving our knowledge of the stellar mass assembly at high redshift allows us to better comprehend or revise cosmological models of galaxy formation and evolution. I found that stellar masses inferred by not taking into account mid-infrared photometry are overestimated by an average value of <Δlog(M*)> = 0.6 dex at 3.5 ≤ z ≤ 12, reaching 2 dex at z > 9. Since one of the codes employed to fit the observed SED allows to account for the emission from an Active Galactic Nucleus (AGN), which can be probed by MIRI, I also carried out additional SED-fitting runs to investigate whether MIR photometry is able to reveal or constraint the presence of an AGN. However, due to a non-optimal setup or AGN libraries, which are not able to reproduce the AGN component, I obtained that, on average, MIRI photometry increases the stellar masses by ~0.3 dex in the range 3 < z < 5. In order to investigate the impact of MIRI on the stellar mass evolution of galaxies, I built the Galaxy Stellar Mass Functions (GSMF) in the redshift range 1.5 ≤ z ≤ 7.5. The GSMFs with and without MIRI photometry are overall compatible, except at higher redshifts, where the number density of galaxies is slightly lower than the one estimated from NIR photometry only. However, since the GSMFs presented in the thesis are derived on a sample non-complete in mass, it is not possible to assess the impact of MIRI photometry on the evolution of the stellar mass of galaxies. The computation of the photometric redshifts including MIR photometry yielded a poorer or, at best, comparable statistic than with optical and NIR photometry due to lack of dust emission templates. The procedure presented in this thesis was then applied to ultra high-redshift candidates, for which I derived photometry from MIRI imaging data to investigate their nature by better characterizing and constraining the SED. This thesis illustrates how MIRI enables new opportunities to better comprehend the stellar mass assembly of galaxies and to search for extreme far objects. However, further efforts to extend the methodology to a larger and statistically significant sample are needed. This will allow to build more detailed GSMFs which will include rare and faint sources. Similarly, additional AGN templates shall be adopted in the fitting procedure and dust emission libraries will be used in the estimation of the photometric redshifts. Finally, follow-up observations are required to confirm the real nature of Ultra High Redshift candidates.