The Galactic worm GW 123.4-1.5: A mushroom-shaped HI cloud

The Dominion Radio Astrophysical Observatory's Synthesis Telescope provides the highest resolution data (1' and 0.82 km s(-1)) to date of an H (I) wor m candidate. Observed as part of the Canadian Galactic Plane Survey, mushro om-shaped GW 123.4-1.5 extends only a few hundred parsecs, contains similar to 10(5) M-circle dot of neutral hydrogen, and appears unrelated to a conv entional shell or chimney structure. Our preliminary Zeus two-dimensional m odels use a single off-plane explosion with a modest (similar to 10(51) erg s) energy input. These generic simulations generate, interior to an expandi ng outer blast wave, a buoyant cloud whose structure resembles the morpholo gy of the observed feature. Unlike typical model superbubbles, the stem can be narrow because its width is not governed by the pressure behind the bla st wave or the disk scale height. Using this type of approach, it should be possible to more accurately model the thin stem and other details of GW 12 3.4-1.5 in the future.