Spatial distribution and energetics of the CII region around M17

Balloon observations of [CII] 158 μm and [OI] 63 μm from the M17 HII region and the molecular cloud complex are presented. Spatial distribution and energetics of the CII region are discussed. Around the M17 HII region, [OI] 63 μm significantly contributes to the cooling of the CII region. Heating due to photoelectric effect of dust grains illuminated by the intence UV radiation can compensate for the cooling due to [CII] and [OI] lines. The CII region extends far beyond the HII region, which indicates the clumpy structure of the CII region. The existence of low-brightness, diffuse [CII] emission component toward M17 SW molecular cloud has been revealed. Distribution of the [CII] emission is quite similar to that of 12CO J=1 → 0 emission. Possible energy source of the [CII] emission is discussed. Ratio of the [CII] luminosity to the total far-infrared luminosity of this diffuse component has been found to exceed that of the intence [CII] emission component around the HII region. (author)