Far-Infrared Spectroscopic Study of Interstellar Medium and Star-formation Rate in the Galactic Center

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We made large-scale survey observations of the far-infrared [CII] spectral line from the Galactic plane, and found that the [CII] line is anomalously weak toward the Galactic center. We attribute this weakness to the soft interstellar radiation field in the Galactic center region. If it is the case, our observations suggest that the current star-formation rate in the Galactic center region is relatively low.In order to check the above suggestion, we planned high spatial observations of the [CII] line emission from the Galactic center using the TIFR (TATA Institute of Fundamental Research, India) 1m balloon-borne telescope, and made the first observation with this system successfully during the campaign in 1999. We could not observe the Galactic center in this campaign, but we are now planning to observe the region on the basis of the experience gained during this campaign.We also observed the Galactic center region with the space-borne telescope ISO (infrared Space Observatory). Although we could not observe the whole region, we could cover the whole far-infrared region spectroscopically, and this observation is complement with balloon-borne observations.We also made theoretical calculations of far-infrared emission from photo-dissociation regions to interpret the above observations.