Loops, Drips, and Walls in the Galactic Chimney GSH 277+00+36

Abstract

We present new high-resolution H I images of the Galactic chimney GSH 277+00+36. The chimney is at a distance of ~6.5 kpc, is more than 600 pc in diameter, and extends at least 1 kpc above and below the Galactic midplane. Using the Australia Telescope Compact Array and the Parkes Radiotelescope as part of the Southern Galactic Plane Survey, we have imaged the H I associated with this chimney, with a spatial resolution of ~6 pc. These are among the highest spatial resolution images of an H I chimney. We find very narrow well-defined shell walls, a remarkably empty interior, and complex small-scale structures. The shell walls show a very steep reduction in emission at the interior edge and a more gradual decline toward the exterior. We suggest that this structure is characteristic of compression and may be used to distinguish stellar by-product shells from shell-like structures resulting from random turbulent motions. The shell and chimney walls also exhibit a great deal of small-scale structure, which we discuss in the context of hydrodynamic instabilities. We find that these structures are primarily cold gas with narrow line widths in the range 1.5-2.5 km s-1.