Astronomical observations of the 807-GHz CO J = 7-6 rotational line with a new heterodyne spectrometer

The submillimeter of carbon monoxide (CO) are a valuable new tool for the study of warm (50 to 500K) molecular material in the interstellar medium. This presence of a large amount of gas with temperatures of a few hundred degrees ear luminous sources has only recently been revealed by far-infrared and submillimeter molecular line observations. The author studied the CO J = 7 → 6 and [CI] 3P2 → 3P1 lines toward several regions with a new heterodyne spectrometer. He reports here the first detection and mapping of CO J = 7 → 6 line emission in the central 10 pc of the Galaxy. The CO 7 → 6 line at 806.65 GHz (372 μm) comes from a dense, clumpy ring or disk (n/sub H2/ ≅ 3 x 104 cm-3, mass ≅ 104 solar masses of temperature ∼300 K. The luminosity of all CO rotational lines emitted from this ∼4' diameter region is about 2 x 104 solar luminosities. CO line emission is a major contribution to the cooling of the interstellar gas near Sqr A. UV radiation from the Galactic center could heat the molecular gas if CO self-shielding is effective. Alternatively, cloud-cloud collisions or mass outflow from the center may cause shocks which heat the war molecular gas. The CO data confirm that neutral ring rotates about the center with a rotation axis close to that of general galactic rotation. The submillimeter CO data also suggest that the velocity centroids along the galactic plane drop by a factor of 1.4 to 2 between 2 and 6 pc from the center