Galactic center molecular clouds. II - Distribution and kinematics

This is a study of the kinematics and distribution of molecular gas near the Galactic center, observed in a variety of millimeter-wave spectral lines. The molecular component is asymmetric with respect to the dynamical center of the Galaxy; about three-fourths of the ¹³CO and CS emission is produced at positive longitudes and a different three-fourths of the gas is at positive velocities with respect to vLSR = 0 km s⁻¹. The velocity field of the gas is highly chaotic, with some clouds having large (>100 km s⁻¹) departures from the velocity pattern expected from purely circular orbits; however, most of the gas (70%) lies in a thin sheet in the Galactic plane. The rotation curve of the gas varies from vrot ≈ 200 km s⁻¹ at l = 5° to no less than vrot ≈ 120 km s⁻¹ near l = 0°. Simple models of the mass distribution within the inner Galaxy are used to compare the observed scale height of the gas with the predicted scale height as a function of galactocentric radius.