Structure and porosity of the multiphase ISM in nearby spatially resolved galaxies

Nearby galaxies observed at high spatial resolution with JWST, ALMA, and MUSE allow us to address fundamental questions related to the influence of young stars on their surrounding interstellar medium (ISM), from giant molecular clouds (GMC; 50 - 200 pc) to galactic scales: How far can ionizing photons travel, and which physical mechanisms favor their escape from HII regions? How do such processes shape the ISM and influence galactic evolution? I will first present constraints on the timescales and physical mechanisms associated with the evolutionary cycle of GMCs in 37 galaxies from the PHANGS-JWST survey, including their dust-embedded star formation phase. We find that the embedded phase of star-formation is short (< 4 Myr) and is drastically reduced in late-type galaxies, hosting GMCs of smaller masses. Strikingly, this phase seems absent in galaxies with a metal-poor ISM, that may host different populations of HII regions, possibly associated with ionizing photon leakage. To further investigate the physics at play in such environments, I will present results obtained using a catalog of HII regions (~70pc) obtained with MUSE in 13 dwarf galaxies, that extend the mass and metallicity range probed by PHANGS. Using multicomponent models to interpret their spectral data, we infer the main physical properties of their HII regions, including the escape fraction of ionizing photons, and assess how the local porosity to UV photons may affect the ISM at larger scales.