Dr. Matilde Mingozzi (Space Telescope Science Institute)

In the current JWST era, detailed observations of the first generation of galaxies are transforming our understanding of the early Universe, revealing both remarkable progress and new puzzles. High-redshift systems in the epoch of reionization (z>6) are typically low-mass, compact, and metal-poor, and they often exhibit prominent emission lines indicative of extreme radiation fields. However, their physical properties remain difficult to constrain: some show evidence for chemical inhomogeneities, and an unexpectedly large fraction may already host actively accreting black holes (AGN) within the first billion years of cosmic time. Nearby blue compact dwarf galaxies share many of these characteristics and therefore provide ideal local laboratories for detailed multi-wavelength investigations of the mechanisms shaping such systems. In this talk, I will present JWST/MIRI-MRS observations of SBS 0335-052, Izw18 and CGCG 007-025, mapping key mid-infrared emission lines (e.g., [Ne II], [S IV], [Ne III], [O IV], [Ne V]) in combination with UV and optical spectroscopy. These data trace ionized gas across multiple ionization states and levels of dust attenuation at sub-kpc scales for the first time in these systems. This analysis enables us to investigate the dominant ionization sources of the gas - massive stars, shocks, or AGN - and reveals extended very high-ionization emission that may be associated with an accreting intermediate-mass black hole. The observations also constrain the presence or absence of dust features such as PAHs, providing the first insights into dust survival in extreme environments. Overall, this study provides us with an extremely powerful toolkit, pivotal for understanding the gas conditions and feedback from different ionization sources in the earliest galaxies that reionized the universe.