We present the peculiar expanding HI shell GSH 138-01-94, discovered in the Canadian Galactic Plane Survey (recently expanded into the International Galactic Plane Survey). This shell is unique because of its unusual location, in the outermost regions of the Galactic disk. The properties of the shell are discussed, as well as possible origins. This leads to the interpreattion that GSH 138-01-94 is probably the remnant of a supernova explosion that occurred 4.3 million years ago in the outer Galaxy. As such, GSH 138-01-94 is the largest, oldest supernova remnant known to date. We relate the peculiar properties of this objects to the special environment in which it was found.
The complete paper is available as electronic preprint
The Canadian Galactic Plane Survey allows a multi-wavelength view of the Galaxy in unprecedented detail. One of the beautiful structures found in the survey data is the expanding shell of hydrogen gas GSH 138-01-94. The name of the shell contains the Galactic coordinates according to guide lines set by the IAU.
GSH 138-01-94 is a very large shell: diameter 360 parsec, more than 1000 lightyears. At this time, the shell is still expanding with a velocity of 11.8 km/s.
More about GSH 138-01-94 on the CASCA 2001 poster
Click on details of the image to learn more
Image prepared by Jayanne English
Colour shades represent observations at different frequencies. Click on a detail in the image to read more about it.
The image shows the shell of atomic hydrogen, radio continuum sources, a molecular cloud, and infrared emission from interstellar dust.
Animation of the 21-cm line data (JAVA)