Galaxies and Cosmology Seminar: Are High Densities Biasing Observed Galaxy Properties? Investigating Nebular Properties in Extreme Conditions Across Cosmic Time

Are High Densities Biasing Observed Galaxy Properties? Investigating Nebular Properties in Extreme Conditions Across Cosmic Time

Deriving observed galaxy properties across cosmic time is an essential tool for understanding galaxy evolution. The advent of JWST is pushing studies of galaxy properties to the earliest galaxies. High-z (z > 6) studies with JWST are finding a host of dense, compact, luminous, highly star-forming galaxies with unusual chemical enrichment unlike anything we observe in the local universe. While a number of physical processes have been examined to explain the extreme properties at high-z, the ionized gas properties remain under-explored. We, therefore, investigate the effects of high-density using a custom grid of Cloudy photoionization models and examine how crucial emission line ratios evolve with density in a uniform-density nebula. We provide fits to ionization parameter diagnostics and ionization correction factors (ICFs), which allow us to account for unobserved ionic species, and determine O/H and UV and optical N/O abundances. We find that, in the absence of a high-ionization density measurement, properties determined using the [O III] λ5007 and [O II] λ3727 lines can be significantly biased due to their lower critical densities. In particular, assuming the low density limit in a high density environment can overestimate [O III] λ4363/λ5007 temperatures by 2200 K, overestimate the log U by 1.13 dex, and underestimate O/H by 0.38 dex. Finally, we discuss the implications of these models on O/H and N/O abundances for a sample of 18 UV N-emitting galaxies spanning 0 < z < 11.