Physical properties of transition regions between atomic and molecular gas in the interstellar medium with the THOR survey
MPIA, Heidelberg, DE
What are the physical properties and the morphology of the transition regions between atomic and molecular gas in giant molecular clouds? Diffuse OH gas has been found previously in transition regions between atomic and molecular gas, and therefore is a promissing tool to investigate these questions.
As part of the THOR project (THOR - The HI, OH, Recombination Line survey of the Milky Way), we map four OH ground state hyperfine transitions (1612, 1665, 1667 and 1720 MHz) in the northern part of the Milky Way (l = 15deg - 67deg, |b|=+/- 1deg) with 20" resolution. We present absorption observations against galactic and extragalactic continuum sources. We determine kinematic properties, optical depth profiles and column densities for each absorption detection. The line ratios of the four transitions give insight into the excitation properties of the diffuse OH gas.
The OH absorption detections are compared to existing galactic surveys in atomic and molecular gas tracers, such as 13CO (GRS), HI absoprtion and emission observations (THOR/VGPS) and dense gas tracers such as HCO+ (BGPS), in order to investigate turbulent properties and ionization levels in different density regimes of molecular and atomic gas. Investigation of OH absorption in different environments, such as their the vicinity to HII regions or SNR, and its location in the galactic plane, will allow us to test influences of external physical processes.
H. Beuter, MPIA, DE
S. Bihr, MPIA, DE
Y. Wang, MPIA, DE
A. Walsh, ICRAR, AT
J. Ott, NRAO, US
and the THOR team