GALACTIC-CENTER MOLECULAR ARMS, RING, AND EXPANDING SHELL .1. KINEMATICAL STRUCTURES IN LONGITUDE-VELOCITY DIAGRAMS

Analyzing the (l, b, V-LSR) data cube of (CO)-C-13(J = 1-0)-line emiss ion from the B ell-Telephone-laboratory survey, we have investigated t he molecular gas distribution and kinematics in the central +/- 1 degr ees (+/- 150 pc) region of the Galaxy. We have applied the pressing me thod to remove the local- and foreground-gas components at low velocit ies in order to estimate the intensity more quantitatively. Two major dense molecular arms have been identified in longitude-radial velocity (l,V) diagrams as apparently rigidly-rotating ridges. The ridges are spatially identified as two arms, which we call the Galactic-Center mo lecular Arms (GCA). The arms compose a rotating ring of radius 120 pc (the 120-pc Molecular Ring), whose inclination is i similar or equal t o 85 degrees. The Sgr B molecular complex is associated with GCA I, an d Sgr C complex is located on GCA II. These arms are as thin as 13 to 15 pc, except for vertically extended massive complexes around Sgr B a nd C. The (l, V) behavior of the arms can be qualitatively reproduced by a model which assumes spiral arms of gas. Assuming a small pitch an gle for the arms, we tried to deconvolve the (l, V) diagram to a proje ction on the galactic plane, and present a possible face-on CO map as seen from the galactic pole, which also reveals a molecular ring and a rms. We have estimated the masses of these molecular features, using t he most recent value of the CO-to-H-2 conversion factor, taking into a ccount its metallicity dependence and radial gradient in the Galaxy. T he estimated molecular masses and kinetic energy are about a factor of three smaller than those reported in the literature using the convent ional conversion factor.