Understanding the multi-phase structure and physical conditions of the ISM in nearby galaxies
Nearby, low metallicity galaxies offer the best laboratories to examine in detail the interplay between stellar activity and a metal-poor interstellar medium (ISM). I will present multi-wavelength Herschel and SOFIA observations of FIR fine structure lines and reveal the physical conditions in the ionized, neutral and molecular gas of nearby star forming regions and galaxies. These diagnostics bring constraints to the fraction of molecular dark gas not traced by CO, the so-called “CO-dark gas”, >75% in the extreme environment of 30 Doradus in the Large Magellanic Cloud. Such a high fraction of CO-dark gas is expected to affect all observations of high-mass star-forming regions. This has important implications for the inferred star formation efficiencies in these environments, the rate at which feedback from massive stars evaporates the reservoir of molecular gas, and the extent to which the associated shielding enable ongoing star formation in other parts of the cloud complex.