Abstract:
Far-infrared fine-structure lines (FIR FSLs) are powerful tracers of high-redshift galaxies and ISM conditions, but key gaps remain in linking FIR FSLs to optical strong lines and in building a consistent framework across local and high-z systems for systematic ALMA–JWST comparisons. In this talk, I will present a comprehensive atlas of global FIR FSL measurements for low- and high-z galaxies spanning diverse types, with extensive ancillary optical and mid-infrared data. Using this dataset, I reassess empirical FIR FSL relations and interpret their physical drivers with photoionization models. I then show what multi-wavelength synthesis enables: constraining AGN contributions to [O III] 88 μm; demonstrating consistent behavior of neutral- and ionized-gas emission across FIR and optical diagnostics; establishing a gas–dust dichotomy that drives “line deficits” in all lines (not only [C II] but also Hα); and quantifying the resulting biases in star-formation-rate estimates for dusty galaxies, motivating an updated view of the ISM.
