Impact of Dust Depletions on BPT Diagrams for Star-forming Regions in Galaxies

The condensation of certain elements into dust grains has several important effects on the Interstellar Medium (ISM), including its heating, cooling, and thermal stability. Grains have a major effect on observed emission line spectra of galaxies because of this feedback. Jenkins’ 2009 study of extinction and depletion of elements resulted in a widely-used model relating a generalized depletion strength F* with element depletions along any line of sight. Our current work streamlines the calculation of post-depleted element abundances predicted by the Jenkins model within the open-access spectral simulation code Cloudy. We explore the effects of varying F* on spectral line ratio predictions from photoionization models. First, we use the benchmark Orion Nebula as a test case, then expand the study to more generalized H II regions. Finally, we select a sample of extragalactic H II regions using spatially resolved data from the MaNGA survey. Our aim is to constrain F* by comparing observations with Cloudy predictions for a range of F* values and other parameters such as metallicity or stellar properties. Our analysis of BPT diagrams and temperature profiles predicted with Cloudy reveal that depletion strength has a significant effect on the predicted emission-line spectrum, the thermal equilibrium, and the structure of the ionized gas. Our BPT diagrams also reveal that an F* value close to 0.5 gives a good representation of the majority of the extragalactic H II regions in our MaNGA sample.