Galaxies are surrounded by large haloes of hot gas which must be replenished as the gas cools. This has led to the concept of galactic 'chimneys'--cavities in the interstellar medium, created by multiple supernova explosions, that can act as conduits for the efficient transport of hot gas from a galaxy's disk to its halo. Here we present a high-resolution map of atomic hydrogen in the Perseus arm of our galaxy, which shows clear evidence for the existence of such a chimney. This chimney appears to have been formed by the energetic winds from a cluster of young massive stars, and may currently have reached the stage of bowing out into the halo.

New observations at high latitudes above the H ii region W4 show that the structure formerly identified as a chimney candidate, an opening to the Galactic halo, is instead a superbubble in the process of fragmenting and possibly evolving into a chimney. Data at high Galactic latitudes (b > 5 • ) above the W3/W4 star forming region at 1420 and 408 MHz Stokes I (total power) and 1420 MHz

We have used polarimetric imaging to study the magneto-ionic medium of the Galaxy, obtaining 1420 MHz images with an angular resolution of 1 over more than 40 square-degrees of sky around the W3/W4/W5/HB 3 H ii region/SNR complex in the Perseus Arm. Features detected in polarization particular, the effects of an extended, low-density ionized halo around the H ii region W4 are evident, probably an example of the extended H ii envelopes postulated as the origin of weak recombination-line emission detected from the Galactic ridge. Our polarization observations can be understood if the uniform magnetic field component in this envelope scales with the square-root of electron density and is 20 µG at the edge of the depolarized region around W4, although this is probably an overestimate since the random field component will have a significant effect.