Abstract

Rest-frame far-ultraviolet (FUV) observations from JWST are currently revolutionizing our understanding of the high-z galaxies that drove reionization and the mechanisms by which they accomplished it. In order to fully interpret these new observations, we must be able to carefully diagnose how properties of the neutral interstellar medium (e.g., column density, covering fraction, outflow velocity) directly relate to the absorption features produced. Using the high-S/N and high-resolution FUV spectra (1050-1800A) of 45 nearby star-forming galaxies from CLASSY, I present the largest uniform, simultaneous characterization of neutral and low-ionization interstellar UV absorption lines (H I, O I, Si II, S II, C II, N II, Al II, Fe II) across a wide range of galaxy properties. I found strong correlations between characteristics of the neutral H I gas within, and around, these galaxies and properties derived from these low-ionization ions. This analysis allowed for the characterization of a new technique for estimating the escape fraction of ionizing photons, as well as provided validation for the previously un-calibrated method based on gas covering fractions. I also found evidence for similar profile shapes between the Lyman alpha emission observed in these galaxies and the stacked absorption profile of these low-ionization ions, demonstrating the intrinsic correlations that exist between the neutral gas distribution and the subsequent escape of ionizing photons.