Large scale distribution of the [CII] fine structure line in the galaxy — ISAS/UA galactic plane survey by balloon

An extensive survey of CII] line emission has been made by using balloon borne telescopes incorporated with a liquid helium cooled Fabry-Perot spectrometer. The observations cover major part of the galactic plane in the first and fourth quadrants as well as some typical HII regions/molecular clouds complexes and a dark cloud. The observed CII] emission is very strong and ubiquitously distributed throughout the galactic plane. The emission should be generated mostly in photo-dissociation region(PDR), but the ionizing and heating UV sources should be well mixed with the molecular clouds, presumably due to clumpy or filamentally structure of the molecular clouds. Some part of the emission may be originated from ELD HII regions which are illuminated by isolated O- and B-stars rather uniformly distributed in interstellar space.