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F. J. Lockman (NRAO)
Several areas around the tangent points of the inner Galaxy have been studied in the 21cm line with the new Green Bank Telescope. The observations have revealed a new population of HI clouds in the Galactic halo. The clouds are coupled dynamically to the disk, and can be found to at least 1.5 kpc from the plane. The clouds are widespread throughout the inner Galaxy in the first and fourth longitude quadrants. A group which has been studied in detail has a median size of a few tens of pc, a median HI mass of 50 solar masses and a median NH of 2 x 1019 . A significant fraction of the neutral mass in the halo may be concentrated in these objects.
Some of the halo clouds have line widths so narrow that the temperature in their cores must be less than 1000 K. Some have HI lines with two velocity components, one broad and one narrow, suggesting that they have a two-phase or core-halo structure. The clouds may have their origin as neutral condensations in a Galactic fountain.
The NRAO is a facility of the National Science Foundation, operated under a cooperative agreement by Associated Universities, Inc.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.