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

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

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...193.6505m&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #65.05; Bulletin of the American Astronomical Society, Vol. 30, p.1340

Astronomy and Astrophysics

Astronomy

Scientific paper

We surveyed the Southern Galactic Hemisphere at b <= -30deg \ in the CO(1--0) emission line to determine the filling factor of molecular gas at high Galactic latitudes and to search for heretofore unknown molecular clouds. The southern Galactic Hemisphere was sampled on a locally-Cartesian grid with 1deg \ (true-angle) spacing in Galactic longitude and latitude. Of the 11,478 points in the sampling grid, the 4982 positions which rise at an elevation >= 30deg \ from Cambridge, MA, the site of the 1.2 m millimeter-wave telescope which was used for the survey, were observed to an rms of Tmb <= 0.2 K. One-hundred-forty-five distinct CO(1--0) emission lines were observed along 135 lines of sight. Of these detections, 71 are new and 74 are associated with 21 previously-cataloged southern hemisphere high-latitude clouds situated within the survey boundaries. The completeness of the survey was estimated to be ~ 70% based on the detection rate of previously known clouds and Monte Carlo simulations. The surface filling factor corrected for the incompleteness of the sampling grid is 0.041, a factor of 10 greater (depending on the cloud-size distribution) than that found in the Northern Galactic Hemisphere at b >= 30(deg) . Adopting as the CO to H_2 conversion ratio NH_2/W_CO = 2.5 x 10(20) cm(-2) [K km s](-1) , the mass surface density of molecular gas in the southern hemisphere at high Galactic latitude is 0.2 M_&sun;\ pc(-2) . The scale height of the 145 detections is ~ 150 pc, greater than the value for local dark and giant molecular clouds. Thus, the high-latitude molecular clouds may be the local analogue of the thick molecular disk observed in the inner Galaxy.

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