Mitchell Institute for Fundamental Physics & Astronomy
College Station, Texas 77843
The intersection between the atomic and molecular interstellar medium (ISM) is still relatively mysterious. In the past two decades, indirect gas tracers such as gamma-ray and dust emission have implied the existence of abundant molecular hydrogen (H2) not traced by our canonical molecular tracer, the CO molecule. In this talk I will review recent efforts in using the OH molecule at 18cm to trace the large-scale Galactic “CO-dark” H2 with the 100m Green Bank Telescope (GBT). I will talk about the serendipitous discovery of an immense amount of dark H2 in the Outer Galaxy in the form of a diffuse disk, co-spatial with the atomic ISM phase. I will also discuss current work combining SOFIA 2.5 THz data and 18cm OH VLA data to constrain the excitation of the OH ground-state and discuss future potential work with mapping OH with radio telescopes around the world.