The Galactic Worm GW 123.4−1.5: A Mushroom-shaped H [CLC][CSC]i[/CSC][/CLC] Cloud

The Dominion Radio Astrophysical Observatory's Synthesis Telescope providesthe highest resolution data (1 arcmin and 0.82 km/s) to date of an HI wormcandidate. Observed as part of the Canadian Galactic Plane Survey,mushroom-shaped GW 123.4-1.5 extends only a few hundred parsecs, contains ~10^5solar masses of neutral hydrogen, and appears unrelated to a conventional shellor chimney structure. Our preliminary Zeus-2d models use a single off-planeexplosion with a modest (~10^{51} ergs) energy input. These generic simulationsgenerate, interior to an expanding outer blast wave, a buoyant cloud whosestructure resembles the morphology of the observed feature. Unlike typicalmodel superbubbles, the stem can be narrow because its width is not governed bythe pressure behind the blast wave nor the disk scale height. Using this typeof approach it should be possible to more accurately model the thin stem andother details of GW 123.4-1.5 in the future.