A Molecular Face‐on View of the Galactic Center Region

We present a method to derive positions of molecular clouds along the lines of sight from a comparison between 2.6 mm CO emission lines and 18 cm OH absorption lines, and apply it to the central region of the Milky Way. With some simple but justifiable assumptions, we derive a face-on distribution of the CO brightness and corresponding radial velocity in the Galactic center without the help of kinematical models. The derived face-on distribution of the gas is elongated and inclined so that the Galactic-eastern (positive longitude) side is closer to us. The gas distribution is dominated by a barlike central condensation, whose size is about 500 × 200 pc. The major axis of the condensation is tilted with respect to the line of sight by an angle of ≃70° (tilted by ≃40–50° from the large-scale stellar bar). This geometry resembles the central regions of barred galaxies. The velocity field shows highly noncircular motion in the central condensation. These characteristics agree with a picture in which the kinematics of the gas in the central hundreds of parsecs of the Galaxy is under the strong influence of a barred potential.