The Far Infrared Lines of OH as Molecular Cloud Diagnostics
Abstract
There are 15 far-IR lines arising between the lowest eight rotational levels of OH and ISO detected nine of them. Furthermore ISO found the OH lines sometimes in emission and sometimes in absorption in a wide variety of galactic and extragalactic objects ranging from AGB stars to molecular clouds to active galactic nuclei and ultra-luminous IR galaxies. This set of OH lines provides a uniquely valuable diagnostic for many reasons: the lines span a wide wavelength range (28.9μm to 163.2μm); the transitions have fast radiative rates; the abundance of the species is relatively high; the IR continuum plays an important role as a pump; the contribution from shocks is relatively minor; and not least the powerful centimeter-wave radiation from OH allows comparison with radio and VLBI datasets. The problem is that the large number of sensitive free parameters and the large optical depths of the strongest lines make modeling the full set a difficult job. We have used a modified SWAS montecarlo radiative transfer code to analyze the ISO/LWS spectra of a number of objects including in both the lines and the FIR continuum; the DUSTY radiative transfer code was used to insure a self-consistent continuum.
- Publication:
-
IAU Joint Discussion
- Pub Date:
- 2003
- Bibcode:
- 2003IAUJD..21E...9S