Self consistent grain depletions and abundances II: Effects on strong-line diagnostics of extragalactic H II regions

The depletion of elements onto dust grains is characterized using a generalized depletion strength F-* for any sightline, and trend-line parameters A(X), B-X, and z(X). The parameters A(X), B-X, and z(X) define the relative depletion pattern, for which values are published in previous works. The present study uses these parameters to calculate post-depleted gas-phase abundances of 15 different elements while varying F-* from 0 to 1. An analysis of emergent strong spectral line intensities, obtained by inputting the calculated abundances into a cloudy model, shows that the depletion strength has a non-trivial effect on predicted emission lines and the thermal balance of the ionized cloud. The amount by which elements deplete also affects the coolant abundances in the gas. Furthermore, it was found that each of the parameters - metallicity, ionization parameter U, and depletion strength F-* have degenerate effects on the emission-line strengths, and thermal balance of the interstellar medium (ISM). Finally, comparing our results to a sample of H II regions using data obtained from the Mapping Nearby Galaxies at Apache Point Observatory survey (MaNGA) revealed that the best-fit F-* was approximately 0.5. However, this best-fitting value does not work well for all metallicities. Removing the sulfur depletion and changing the nitrogen abundance pattern can improve the fit. As a result, extra observational evidence is required to verify the choices of parameters and better constrain the typical depletion strength in galaxies.

Automated summary

The study investigates the depletion strength's effect on emission lines and thermal balance of the ionized cloud. It also finds that the parameters - metallicity, ionization parameter U, and depletion strength F-* - have mutual effects on the emission-line strengths and thermal balance of the interstellar medium (ISM). Comparing the results to H II regions, the best-fit F-* is approximately 0.5 but may not be suitable for all metallicities.