Abstract
Understanding the physics of the interstellar medium is critical for understanding star formation, its feedback, and AGN feedback. Line ratio diagnostics diagrams, such as BPT diagrams, have been extensively used to study the ISM. However, their limitations hide inaccuracies of photoionization models, leading to a number of discrepant results in the literature on metallicity, abundance pattern, and correlations between metallicity and ionization parameters. We present a new perspective about line ratio diagnostics that would help resolve these discrepancies and constrain the undertested assumptions in photoionization models. It also helped us discover surprisingly that the dust attenuation correction of forbidden lines are different from our past expectations. This new perspective should pave the road towards an era in which we can model the astrophysics of the warm ionized gas with precision, in the same style as precision cosmology. I will also introduce the design of a cost-effective, high spectral resolution, integral field spectrograph. When paired with a small telescope like a telephoto lens or arrays of them, it could provide unprecedented data to help us better understand star-forming HII regions and the feedback of star formation.
