CO J = 3-2 OBSERVATIONS OF THE NEUTRAL DISK IN SAGITTARIUS A WEST

We have studied the distribution of CO J = 3-2 emission from the dense neutral disk in Sgr A West. The distribution observed is similar to that seen in the low-excitation CO J = 1-0 line but shows a stronger concentration toward the central higher excitation regions of the disk. The regions of strongest CO J = 3-2 emission correspond closely with those seen in high-excitation transitions such as CO J = 7-6 and HCN J = 1-0. The disk is highly clumped as may be seen from the strongly saturated behavior of the CO line intensities. Inferred CO column densities through individual clumps are as high as 2 × 1019 cm-2, whereas typical beam-averaged column densities are more like 2 × 1018 cm-2. The excitation implies gas kinetic temperatures in the range T = 100-200 K, somewhat lower than temperatures inferred from metastable NH3 observations. Densities are found to range from 2 × 104 cm-3 up to at least 2 × 105 cm-3, in good agreement with the densities derived from HCN and CS. The kinematic structure shows gas in relatively simple circular motion about the center as well as substantial evidence for considerable noncircular motions. A number of well-delineated clouds have motions apparently unconnected with the dominant pattern of circular rotation. These clouds account for about 6% of the mass of the high-velocity gas. For that gas participating in circular rotation the rotation curve is found to be relatively flat between 2 and 8 pc. The mass enclosed within the central 2 pc radius is estimated to be 5.6 × 106 M⊙. The flat rotation curve implies a substantial distributed mass of 1.5 × 107 M⊙ between 2 and 8 pc.