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S. J. Gibson, A. R. Taylor (U. Calgary), L. A. Higgs (HIA)
Cold atomic gas is often observable at 21cm as HI self-absorption (HISA) against background HI emission. However past investigations have been limited in either angular resolution or sky coverage, making an unbiased assessment of the HISA population difficult. We are carrying out the first wide-field synthesis imaging study of HI self-absorption as part of the Canadian Galactic Plane Survey, mapping over 650 square degrees between longitudes of 74 and 147 at 1-2 arcminute scales.
We present an overview of the HISA identified to date, along with a discussion of our automated detection and analysis methods. Though ongoing, our survey has already revealed a large number of dark and intricate features. These show a strong tendency to cluster near velocities tracing spiral structure. At the same time, the self-absorption also displays considerable independence from 12CO emission features, contrary to the traditional view of HISA being produced by small amounts of atomic gas in predominantly molecular clouds.
This work is supported by a grant from the Natural Sciences and Engineering Research Council of Canada.
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The author(s) of this abstract have provided an email address for comments about the abstract: gibson@ras.ucalgary.ca