Fermi Gamma-ray Space Telescope

Thermal OH Emission: A New Probe of Galaxy Structure

P. D. Engelke
R. J. Allen, D. E. Hogg

Abstract:

Recent GBT observations have shown that high-sensitivity measurements of thermal OH emission can be a useful alternative tracer for the large-scale distribution of molecular gas in the Galactic ISM with a greater spatial distribution when compared with CO. It appears likely to be tracing the 'dark' gas detected by Grenier et al. (2005) in gamma ray emission from cosmic ray interactions. Unlike those measurements, the thermal OH emission provides information about the distance and kinematics of this molecular component of the ISM. We apply this new tool to two questions about the molecular structure of the Perseus Arm: the thickness in the Z-direction, and the rolling motions of the arm discovered earlier in HI.