A complete survey of the central molecular zone in NH3

We present a map of the major part of the central molecular zone (CMZ) of simultaneous observations in the NH3 (J, K) = (1,1) and (2,2) lines using the Kagoshima 6 m telescope. The mapped area is -1.degrees 000 >= I <= 10625 and -0.degrees 375 <=< b <= 0.degrees 0250. The kinetic temperatures derived from the (2,2) to (],I) intensity ratios are 20-80 K, or exceed 80 K. The gases corresponding to temperatures of 20-80 K and >= 80 K contain 75% and 25% of the total NH3 flux, respectively. These temperatures indicate that the dense molecular gas in the CMZ is dominated by gas that is warmer than the majority of the dust present there. A comparison of our observations with a CO survey by Sawada et al. (200 1, ApJS, 136, 189) shows that the NH3 emitting region is surrounded by a high-pressure region on the longitude-velocity (1-v) plane. Although NH3 emission traces dense gas, it does not extend over a high-pressure region. Therefore, the high-pressure region is less dense and has to be hotter. This indicates that the molecular-cloud complex in the Galactic center region has a "core" of dense and warm clouds that are traced by the NH3 emission, and an "envelope" of less-dense and hotter gas clouds. Besides heating by ambipolar diffusion, the hot plasma gas emitting the X-ray emission may heat the hot "envelope".