We present a map of the major part of the central molecular zone ( CMZ ) of simultaneous observations in the NH _ { 3 } ( J,K ) = ( 1,1 ) and ( 2,2 ) lines using the Kagoshima 6-m telescope .
The mapped area is \timeform { -1 D .000 } \leq l \leq \timeform { 1 D .625 } , \timeform { -0 D .375 } \leq b \leq \timeform { +0 D .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 temperature of 20–80 K and \geq 80 K contain 75 % and 25 % of the total NH _ { 3 } 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 with the CO survey by \citet sawada shows that the NH _ { 3 } emitting region is surrounded by a high pressure region on the l - v plane .
Although NH _ { 3 } emission traces dense gas , it is not extended into 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 which are traced by the NH _ { 3 } 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 ” .