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S.T. Strasser, J.M. Dickey (University of Minnesota), A.R. Taylor (University of Calgary)
We have obtained neutral hydrogen (HI) absorption spectra with the highest possible spectral and spatial resolution using the VLA (0.2 km/s and 1.5 arcsec). Five lines of sight towards continuum background sources were selected from a sample of over 400 in the Canadian Galactic Plane Survey (CGPS). We selected these lines of sight because they contain the narrowest absorption lines in the CGPS (width less than 2 km/s) . Only one of the lines has a corresponding CO emission feature, and none have an HI Self-Absorption (HISA) counterpart. The new VLA observations allow us to get a very accurate measure of the Doppler width of the lines, which can then be compared to the width and spin temperature in the CGPS. This work allows us to compare methods of measuring cold HI temperatures at two quite different resolutions for clouds with extraordinary properties. We identify these clouds as possible links between the molecular and cool neutral hydrogen phases. Our study also helps us answer the question of whether or not we miss information in surveys such as the CGPS that is contained in much higher resolution spectra.
The author(s) of this abstract have provided an email address for comments about the abstract: strasser@astro.umn.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.