COBE/DIRBE Survey of Molecular Gas at High Galactic Latitude
Session 57 -- COBE and Related Papers
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

## [57.09] COBE/DIRBE Survey of Molecular Gas at High Galactic Latitude

W.T.Reach (USRA), W.F.Wall (INAOE), M.G.Hauser (NASA/GSFC), T.J.Sodroski (ARC), N.Odegard,J.L.Weiland (GSC)

We use observations by the COBE $^1$ Diffuse Infrared Background Experiment (DIRBE) to determine the amount and distribution of molecular gas at high galactic latitude. Previous estimates based on surveys of H$_2$ absorption lines were limited by the number of hot stars; surveys of extinction of background starlight were limited by nonuniformity of the background and sensitivity. Infrared surface brightness can be used as a tracer of the total column density of interstellar material. This technique was previously employed with the IRAS 100 $\mu$m and Hat Creek 21-cm line surveys. Followup observations failed to reveal CO emission from the inferred molecular clouds, leading to the suspicion that the infrared excess was not accurately tracing molecular gas, tracing instead dust temperature variations. We used the DIRBE observations at 100, 140, and 240 $\mu$m to determine the dust temperature and column density throughout the sky with a 0.7$^\circ$ beam. The column density was then compared to the Hat Creek, Bell Labs, and other 21-cm line surveys in order to determine the dust-to-atomic gas abundance ratio. The excess dust abundance with respect to a spatially averaged map of the dust-to-gas ratio was identified as molecular gas. We present maps of the inferred molecular gas distribution, and compare to recent surveys of the extent of molecular gas at high galactic latitude.

\noindent $^1$The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) is responsible for the design, development, and operation of the Cosmic Background Explorer (COBE ). Scientific guidance is provided by the COBE Science Working Group. The COBE program is supported by the Astrophysics Division of NASA's Office of Space Science.