Galactic-Center Molecular Arms, Ring, and Expanding Shell. II. Expanding Molecular Shell

We consider the three-dimensional structure of the so-called 200-pc expanding molecular ring in the Galactic Center by analyzing the (b, V_LSR) diagrams of the (13) CO(J = 1--0) line emission from the Bell-Telephone-Laboratory survey. We show that the (b, V) features can be fitted by a spheroidal shell pinched at the equator (dumbbell-shaped shell), which we call the expanding molecular shell (EMS). The radius is about 180 pc and the vertical extent is more than +/- 50 pc. The shell is expanding at 160 km s(-1) , and is rotating at 70 km s(-1) . The association of the radio continuum emission indicates that the EMS is a mixture of molecular and ionized hydrogen gases. An extended hot (X-ray) plasma appears to fill the interior of the shell. The estimated molecular mass of the shell is ~10(7M_{sun) and its kinetic energy ~2 times 10(54)erg.