Large-Scale Far-Infrared Spectroscopic Study of the Galactic Center Region with High Spatial Resolution

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Our previous balloon-borne observations revealed that the far-infrared [CII] line is systematically weak toward the Galactic center. We proposed a hypothesis that this weakness of the [CII] line can be attributed to the soft interstellar radiation field in the Galactic center. This hypothesis can also explain the ubiquitousness of warm molecular clouds in the region. Moreover, this hypothesis leads to an interesting prediction that the star-formation rate in the Galactic center region is low.However, most of the above discussions relied on observation with very poor spatial resolution, and high-spatial observations had been long-awaited.In order to check the above hypothesis, we performed high-spatial resolution observations of the far-infrared [CII] line using a balloon-borne telescope. This is a joint project with the Tata Institute of Fundamental Research (TIFR) in India. TIFR is in charge of the 1m balloon-borne telescope, and the Japanese group is in charge of the far-infrared Fabry-Perot spectrometer.We performed two balloon flights in the period of the fiscal year from 2000 to 2002, and made high-spatial spectroscopic observations of Galactic star-forming regions. Furthermore, we analyzed observational results of our previous balloon observations and previous space-borne missions. We thereby obtained very important information to understand the effects of radiation field on interstellar clouds.Through these activities, we made detailed study of interaction between interstellar radiation field and interstellar matter as a basis of the understanding the physical processed in the Galactic center.