Astroskiagraphy of Cold Galactic H I

S. J. Gibson, A. R. Taylor (U. of Calgary)
C. M. Brunt, P. E. Dewdney, L. A. Higgs (HIA)

A skiagram is an image made up of shadows or outlines. Much of the cold atomic hydrogen in the interstellar medium can only be studied skiagraphically as H I self-absorption (HISA) against background H I 21cm emission. The Canadian Galactic Plane Survey (CGPS) has captured a multitude of HISA features, many of which are invisible in prior surveys at lower resolution.

We are charting the distribution of HISA clouds in a 73 x 9 degree section of the outer Galaxy covered by the CGPS. We have developed automated methods of detecting and analyzing HISA which allow us to study the cloud population systematically. We report on the latest results of our survey, including the gas properties of HISA features, their total mass budget, spatial distribution, and degree of statistical association with detected molecular gas. We also consider issues of feature detectability and possible biases in our approach.

This work is supported by a grant from the Natural Sciences and Engineering Research Council of Canada.