Molecular Face-on View of the Galactic Centre: A Molecular Face-on View of the Galactic Centre Region

Tsuyoshi Sawada,1,2,3 Tetsuo Hasegawa,2,3 Toshihiro Handa3 and R. J. Cohen4, 1Nobeyama Radio Observatory, 462-2 Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305, Japan, 2National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan, 3Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan, 4Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire SK11 9DL

Paper: MNRAS, accepted


EPrint Server: astro-ph/0401286


We present a method to derive positions of molecular clouds along the lines of sight from a quantitative comparison between 2.6 mm CO emission lines and 18 cm OH absorption lines, and apply it to the central kiloparsecs 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 centre without any 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 apparent size is 500* 200 pc. A ridge feature is seen to stretch from one end of the central condensation, though its elongated morphology might be artificial. The velocity field shows clear signs of noncircular motion in the central condensation. The `expanding molecular ring' feature corresponds to the peripheral region surrounding the central condensation with the Galactic-eastern end being closer to us. These characteristics agree with a picture in which the kinematics of the gas in the central kiloparsec of the Galaxy is under a strong influence of a barred potential. The face-on distribution of the in situ pressure of the molecular gas is derived from the CO multiline analysis. The derived pressure is found to be highest in the central 100 pc. In this region, the gas is accumulating and is forming stars.

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