We present a detailed study of molecular gas in the central 10 pc of the Galaxy through spectral line observations of four rotation inversion transitions of NH _ { 3 } made with the Very Large Array .
Updated line widths and NH _ { 3 } ( 1,1 ) opacities are presented , and temperatures , column densities , and masses are derived for the major molecular features .
We examine the impact of Sgr A East on molecular material at the Galactic center and find that there is no evidence that the expansion of this shell has moved a significant amount of the 50 km s ^ { -1 } giant molecular cloud .
The western streamer , however , shows strong indications that it is composed of material swept-up by the expansion of Sgr A East .
Using the mass and kinematics of the western streamer , we calculate an energy of E _ { SN } = ( 2 - 9 ) \times 10 ^ { 51 } ergs for the progenitor explosion and conclude that Sgr A East was most likely produced by a single supernova .
The temperature structure of molecular gas in the central \sim 20 pc is also analyzed in detail .
We find that molecular gas has a “ two-temperature ” structure similar to that measured by on larger scales .
The largest observed line ratios , however , can not be understood in terms of a two-temperature model , and most likely result from absorption of NH _ { 3 } ( 3,3 ) emission by cool surface layers of clouds .
By comparing the observed NH _ { 3 } ( 6,6 ) -to- ( 3,3 ) line ratios , we disentangle three distinct molecular features within a projected distance of 2 pc from Sgr A* .
Gas associated with the highest line ratios shows kinematic signatures of both rotation and expansion .
The southern streamer shows no significant velocity gradients and does not appear to be directly associated with either the circumnuclear disk or the nucleus .
The paper concludes with a discussion of the line-of-sight arrangement of the main features in the central 10 pc .