Dark gas in the Diffuse Interstellar Medium
131 Campbell Hall
Bill Reach (URSA)
The diffuse interstellar medium contains more molecular gas than had been appreciated before the discovery of "dark gas," which is evident when subtracting atomic gas from the total amount of material, presumed to be traced either by far-infrared dust thermal emission or gamma-rays from cosmic ray-nucleon interactions. Using the Planck far-infrared and Arecibo GALFA 21 cm line surveys, we identified a set of isolated interstellar clouds (approximately degree-sized on the sky and comprising 100 solar masses) in order to locate the "dark gas" and enable follow-up to probe its nature. In this talk I will describe the possible nature of the dark gas as H2 untraced by CO, or cold HI untraced by 21-cm emission, or dust property variations.