Observations of Galactic Carbon Monoxide Emission at 2.6 Millimeters

Abstract

A wide variety of galactic sources have been observed at 2.6 mm (115,271.2 MHz) to determine the extent and strength of interstellar 12C16O. Extended regions of CO emission were found in the direction of 32 H ii regions and five supernova remnants. The CO emission was found to be larger in spatial extent than the 6-cm continuum H ii emission, and CO emission maxima appear to be related to continuum emission peaks and infrared sources in several sources. Except near optically dark nebulae, little CO emission was detected away from the galactic plane. Radial velocities of the CO emission are within 10 km s ' of the OH, H ii (l09a), and H2CO velocities measured by other observers for the same sources. 13C16O was also measured in many of the stronger sources. The optical depths calculated for `2C'6O range between 20 and 120, if the terrestrial value of 1/89 is assumed for the ratio of 13C/12C. For excitation temperatures in the range of 10 -50 K, the calculated projected densities range from 1018 to 2.5 x 1019 molecules cm-2. Subject headings: molecules, interstellar - nebulae - radio sources