The Galactic Worm GW 123.4-1.5: A Mushroom-shaped H i Cloud.

Abstract

The Dominion Radio Astrophysical Observatory's Synthesis Telescope provides the highest resolution data (1&arcmin; and 0.82 km s-1) to date of an H i worm candidate. Observed as part of the Canadian Galactic Plane Survey, mushroom-shaped GW 123.4-1.5 extends only a few hundred parsecs, contains approximately 105 M middle dot in circle of neutral hydrogen, and appears unrelated to a conventional shell or chimney structure. Our preliminary Zeus two-dimensional models use a single off-plane explosion with a modest ( approximately 1051 ergs) energy input. These generic simulations generate, interior to an expanding outer blast wave, a buoyant cloud whose structure resembles the morphology of the observed feature. Unlike typical model superbubbles, the stem can be narrow because its width is not governed by the pressure behind the blast 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 123.4-1.5 in the future.