Tracing the Interstellar Medium with [CII], [NII], and CO"
1 LeConte Hall
Paul Goldsmith (JPL)
The [CII] 158um line is an important tracer of several critical stages of the evolution of the interstellar medium (ISM) and star formation. It has been widely observed in a large number of distant galaxies with Herschel and ALMA. But detailed observations of the [CII] line and other tracers in the local universe are a requirement for the interpretation of these observations of distant galaxies. We present a study of the distribution of the [CII] line in the plane of the Milky Way. This study has been made possible with spectrally resolved observations of [CII] in the Milky Way with the HIFI instrument on Herschel, as part of the GOT C+ Open Time Key Program. We use the [CII] emission to derive, together with observations of HI, CO, and 13CO, the Galactic distribution of the different phases of the ISM. We also present preliminary results from a Galactic Plane survey of [NII] fine structure emission. Recently-analyzed [CII] observations with Herschel and SOFIA indicate some potentially important effects related to absorption of [CII] by the diffuse interstellar medium and by dust in GMCs. We discuss these in terms of their possible impact on understanding emission from very luminous infrared galaxies.