2007PASJ...59..869N

begin{HTML}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 6m telescope. The mapped area is -1°.000 <= l <= 1°.625 and -0°.375 <= b <= 0°.250. The kinetic temperatures derived from the (2,2) to (1,1) 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. (2001, ApJS, 136, 189) shows that the NH₃ emitting region is surrounded by a high-pressure region on the longitude-velocity (l - 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 NH<sub>3</sub> 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''.