A Survey of High‐Latitude Molecular Gas in the Southern Galactic Hemisphere

To determine the distribution of molecular gas at high Galactic latitudes, nearly one-half of the southern Galactic hemisphere at b ≤ -30 ° was surveyed in the CO (1-0) transition at 115 GHz. The sampling was done on a locally Cartesian grid with 1° (true angle) spacing in Galactic longitude and latitude. Of the 11,478 points in the grid, the 4982 that rise above an elevation of 30° in Cambridge, Massachusetts, the site of the 1.2 m millimeter-wave telescope used for the survey, were observed to an rms of T ~ 0.1 K. We found 144 distinct CO (1-0) emission lines along 133 lines of sight. Of these detections, 58 are new and 75 are associated with 26 previously cataloged high-latitude molecular clouds situated within the survey boundaries. The surface filling factor of molecular gas is 0.03, a factor of 10 greater than that found in the northern Galactic hemisphere at b ≥ +30 ° . On the assumption that the CO/H 2 ratio [ N (H 2 )/ W (CO)] is given by 1.0 × 10 20 cm -2 (K km s -1 ) -1 , the mass surface density of molecular gas in the region of the survey is 0.09 M ☉ pc -2 . The Gaussian scale height of the 133 detections is ~100 pc, consistent with that determined for lower latitude dark clouds.