Contributed Talk - Splinter RadioSky
Molecular absorption spectroscopy in the Southern Galactic plane: Synergies between FIR and radio wavelengths
Arshia Maria Jacob, Karl M Menten
Johns Hopkins University, Baltimore, USA
While the absorption spectra of the sub-mm and FIR wavelength transitions of CH provide robust tools for measuring column densities, their observations are limited and, moreover, expensive because they require space- or air-borne instrumentation. This turns our attention toward other viable transitions of CH and in particular the three radio wavelength (9 cm) hyperfine-structure (HFS) splitting lines between the Lambda-doublet components of its rotational ground state. Despite being ubiquitously observed the excitation conditions of this component were found to be inconsistent with assumptions of local thermodynamic equilibrium (LTE) and further complicated by level inversion. Anchored by constraints from its FIR rotational lines, I will discuss the excitation as well as the physical conditions traced by CH. The results of which will greatly validate the use of the easily observable ground state HFS lines of CH as a powerful radio wavelength probe of the diffuse and translucent interstellar medium, alongside the 21 cm HI, the 18 cm OH, and the 6 cm H2CO lines.