Observational consequences of fine structure line optical depths on infrared spectral diagnostics
Abstract
It has long been known that infrared fine structure lines of abundant ions, like the [O III] 88 micron line, can become optically thick in H II regions under certain high luminosity conditions. This could mitigate their potential as diagnostic tools, especially if the source is too dusty for optical spectroscopy to otherwise determine the system's parameters. We examined a series of photoionization calculations which were designed to push the nebulae into the limit where many IR lines should be quite optically thick. We find that radiative transfer effects do not significantly change the observed emission line spectrum. This is due to a combination of grain absorption of the hydrogen ionizing continuum and the fact that the correction for stimulated emission in these lines is large. Given these results, and the likelihood that real objects have non-thermal line broadening, it seems unlikely that line optical depth presents a problem in using these lines as diagnostics of the physical conditions or chemical composition.
Keywords
Cite
@article{arxiv.astro-ph/0211463,
title = {Observational consequences of fine structure line optical depths on infrared spectral diagnostics},
author = {Nicholas Abel and Adam Bryant and Prabodh Dhakal and Ashley Gale and Alva Gibson and William Goddard and Chad Howard and Ameya Kolarkar and Pey Lian Lim and Gargi Shaw and Gary Ferland},
journal= {arXiv preprint arXiv:astro-ph/0211463},
year = {2009}
}
Comments
16 pages, 4 figures, to be published in the February 2003 issue of the PASP