CO 7-6 submillimeter emission from the galactic center - Warm molecular gas and the rotation curve in the central 10 parsecs

Abstract

Bright CO J = 7-6 submillimeter line emission in the central 10 pc of the Galaxy has been mapped. This is the first detection of the 7-6 line from the Galactic center; it was made with a new submillimeter heterodyne spectrometer mounted on the 3.0-m NASA IRTF telescope at Mauna Kea, Hawaii. The 372-micrometer CO emission comes from a dense, clumpy disk (10,000 solar masses) of temperature about 300 K. The luminosity of all CO rotational lines emitted from this approximately 4-arcmin diameter region is about 20,000 solar luminosities. CO line emission is a major contribution to the cooling of the interstellar gas near Sgr A. The CO data show that the rotational velocities drop by a factor of 1.4 to 2 between 2 and 6 pc from the center. The rotation curve is consistent with a 'Keplerian' fall off around a point mass and implies that most of the mass is in a more compact distribution than an isothermal stellar cluster. Broad line width emission toward the central 30 arcsec of the Galaxy indicates that there is a significant amount of molecular material in the inner, mostly ionized, cavity.