Galactic Observations of Terahertz C+(GOT C+): [CII] Detection of Warm “Dark Gas” in the ISM

Abstract

The Herschel HIFI Key Program, G alactic O bservations of T erahertz C + ( GOT C+ ) is a survey of [CII] 1.9 THz emission throughout the Galaxy. Comparison of the first results of this survey with HI and CO isotopomer emission reveals excess [CII] emission beyond that expected from HI and CO layers alone, and is best explained as coming from a hidden layer of H 2 gas, the so-called ISM “dark gas”.