Kinematics of carbon monoxide observed within one degree of the galactic center

Observations of the inner 2° of galactic longitude have been made in the 2.6 mm transition of carbon monoxide with T-2' beam spacings.The resulting maps show several large scale (>100 pc) patterns which correlate well with features present in H i, including the nuclear disk and the 3 kpc arm.Several features are identified with absorption by very cold foreground clouds; the 3 kpc arm feature occurs in both emission and absorption.Subject headings: galaxies: Milky Way -galaxies: nuclei -galaxies: structure -II.OBSERVATIONS The observations were made during 1975 May and July at the 36 foot (11 m) radio telescope of the National Radio Astronomy Observatory on Kitt Peak.The single-sideband noise temperature of the cooled-mixer receiver was ~800 or ~1500K (including the atmosphere), with the larger value occurring during July.All observations were taken through clear skies.The filter bank consisted of 256 channels, each of 1 MHz (2.6 km s" 1 ) width and separated by 1 MHz: the total velocity coverage of 650 km s" 1 is sufficiently large to include all known emission from the nuclear region.Because no matching of partial spectra was required, the observations are quite sensitive to broad, weak features.We observed in the position-switching mode by moving the telescope during each observation (of 10 minutes duration) to a reference position at a, 6(1950) = 17 h 34 m 39 s , -26°29T7".This direction was itself carefully observed and determined to be free of CO emission.In spite of the sensitivity of the cooled receiver to changes in elevation during the position-switching cycle, the baselines of the profiles were generally quite flat.In a few cases, linear baselines were subtracted from an entire spectrum.We observed along several strips of longitude, generally at 1' intervals at |A/| < 10', and at either 2' or 5' intervals outside this range.The displacements A/ and A6 are measured with respect to the peak in 2 /xm radiation in the direction of Sgr A (West) at / = -00°03'20", b = -00 o 02'45" (Rieke and Low 1973).This position evidently corresponds to that of the peak of the distribution of normal stars, and thus to the direction of the dynamical center of the Galaxy.The * Operated by Associated Universities, Inc., under contract with the National Science Foundation.