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Arxiv: On the Interpretation of Mid-Infrared Absorption Lines of Gas-Phase H_2O as Observed by JWST/MIRI Published: 6/7/2024 9:29:13 PM Updated: 6/7/2024 9:29:13 PM

Paper abstract: Ro-vibrational absorption lines of H_2O in the 5-8 \mum wavelength rangeselectively probe gas against the mid-infrared continuum emitting background ofthe inner regions of YSOs and AGN and deliver important information about thesewarm, dust-obscured environments. JWST/MIRI detects these lines in many linesof sight at a moderate spectral resolving power of R~3500 (FWHM of 85km/s). Based on our analysis of high-resolution SOFIA/EXES observations, wefind that the interpretation of JWST/MIRI absorption spectra can be severelyhampered by the blending of individual transitions and the lost information onthe intrinsic line width or the partial coverage of the background continuumsource. In this paper, we point out problems such as degeneracy that arise inderiving physical properties from an insufficiently resolved spectrum. This canlead to differences in the column density by two orders of magnitude. Weemphasize the importance of weighting optically thin and weak lines in spectralanalyses and provide recipes for breaking down the coupled parameters. We alsoprovide an online tool to generate the H_2O absorption line spectra that canbe compared to observations.