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To determine the distribution of molecular gas at high Galactic latitudes, nearly one-half of the southern Galactic hemisphere at b ¹ [30¡ was surveyed in the CO (1È0) 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 K. We found 144 distinct CO (1È0) emission lines along 133 lines of sight. Of these T A * D 0.1 detections, 58 are new and 75 are associated with 26 previously cataloged high-latitude molecular clouds situated within the survey boundaries. The surface Ðlling factor of molecular gas is 0.03, a factor of 10 greater than that found in the northern Galactic hemisphere at b º ]30¡. On the assumption that the ratio is given by 1.0 ] 1020 cm~2 (K km s~1)~1, the mass surface density of CO/H 2 [N(H 2 )/W (CO)] molecular gas in the region of the survey is 0.09 pc~2. The Gaussian scale height of the 133 detec-M _ tions is D100 pc, consistent with that determined for lower latitude dark clouds.

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We surveyed the northern Galactic hemisphere (NGH) at b º 30¡ in the CO (1È0) emission line to determine the surface Ðlling factor of molecular gas at high Galactic latitudes and to search for heretofore unknown molecular clouds. The NGH was sampled on a locally Cartesian grid with 1¡ (trueangle) spacing in Galactic longitude and latitude. Of the 11,478 points in our grid, we observed all 10,562 positions that rise to an elevation above 30¡ in Cambridge, MA, the site of the 1.2 m millimeterwave telescope that was used for the survey. Only 26 lines of sight showed CO emission. Monte Carlo simulations based on our sampling grid and with cloud sizes, in a uniform distribution, ranging from 0 to 2 deg2 suggest that the survey is D70% complete. Power-law distributions yield fractional completenesses that are typically a factor of 2 lower. The surface Ðlling factor, corrected for the incompleteness of our sampling grid, is 0.004È0.008, depending on which cloud size distribution is used. These values are substantially lower than what is found in the southern Galactic hemisphere at b ¹ [30¡. Adopting as the CO to conversion ratio cm~2 (K km s~1)~1, the mass surface density of H 2 N H2 /W CO \ 2.5 ] 1020 molecular gas in the north ranges from 0.015^0.009 to 0.035^0.020 pc~2. With the exception of M _ four fairly signiÐcant aggregations of clouds (the complexes associated with the Polaris Ñare, Ursa Major, Draco, and L134), and a handful of isolated cloudlets, the northern Galactic hemisphere at b º 30¡ is found to be largely free of molecular gas.

We present results from an initial survey of the 2(12)-1(11) transition of formaldehyde (H2CO) at 140.8 GHz in giant molecular clouds in the far outer Galaxy (RG >or= 16 kpc). Formaldehyde is a key prebiotic molecule that likely plays an important role in the development of amino acids. Determining the outermost extent of the H2CO distribution can constrain the outer limit of the Galactic Habitable Zone, the region where conditions for the formation of life are thought to be most favorable. We surveyed 69 molecular clouds in the outer Galaxy, ranging from 12 to 23.5 kpc in galactocentric radius. Formaldehyde emission at 140.8 GHz was detected in 65% of the clouds. The H2CO spectral line was detected in 26 of the clouds with RG > 16 kpc (detection rate of 59%), including 6 clouds with RG > 20 kpc (detection rate of 55%). Formaldehyde is readily found in the far outer Galaxy-even beyond the edge of the old stellar disk. Determining the relatively widespread distribution of H2CO in the far outer Galaxy is a first step in establishing how favorable an environment this vast region of the Galaxy may be toward the formation of life.

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The conversion factor, between the velocity-integrated CO(1È0) antenna temperature, W (CO), X CO , and the column density, is determined for 32 positions in two translucent high-latitude molec-H 2 N(H 2 ), ular clouds, MBM 40 and MBM 16.is calculated using CH observations of theThe latter quantity, divided by W (CO) yields for various posi-N(H 2 ). X CO tions across the clouds. We observed 24 positions in MBM 16, and values were derived in the range X CO (1.6È17.3) ] 1020 cm~2 (K km s~1)~1, with a mean value of 7.6 ] 1020. Eleven lines of sight were sampled in MBM 40 yielding values of in the range (0.7È9.7) ] 1020, with a mean value of X CO 2.6 ] 1020. An inverse relationship between and W (CO) may exist, suggesting that the variation in X CO for these two translucent clouds arises from varying CO abundances. This paper also reports the X CO existence of a broad component in the CH spectra observed throughout much of MBM 16. This component possibly originates in the disturbed outer regions of the cloud where the gas is not gravitationally bound to the core of the cloud. It is unclear how sensitive the CO rotational transitions are to this component, but it is likely that the ratio in this broad-line gas is less than 10~5. However, if the CO/H 2 ratio is the same for the gas in the extended wings as it is for the typical cloud gas, then up to CH/H 2 40% of the cloud mass could be contained in this difficult to trace molecular component.