Evidence for chimney breakout in the Galactic supershell GSH 242 - 03 + 37

We present new high resolution neutral hydrogen (H i) images of the Galactic supershell GSH 242-03+37. These data were obtained with the Parkes Radiotelescope as part of the Galactic All-Sky Survey (GASS). GSH 242-03+37 is one of the largest and most energetic H i supershells in the Galaxy with a radius of 565 ± 65 pc and an expansion energy of 3 × 10 ergs. Our images reveal a complicated shell with multiple chimney structures on both sides of the Galactic plane. These chimneys appear capped by narrow filaments about 1.6 kpc above and below the Galactic mid-plane, confirming structures predicted in simulations of expanding supershells. The structure of GSH 242-03+37 is extremely similar to the only other Galactic supershell known to have blown out of both sides of the plane, GSH 277+00+36. We compare the GASS H i data with X-ray and H-α images, finding no strong correlations. Subject headings: surveys — Galaxy: structure — ISM: structure — ISM: Bubbles — ISM: H i Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW 1710, Australia; [email protected] Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn VIC 3122, Australia Remote Sensing Division, Naval Research Laboratory, Code 7213, 4555 Overlook Ave. SW, Washington, D.C, 20375 National Research Council Postdoctoral Fellow Laboratoire d’Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire, CH1290, Sauverny, Switzerland Centre for Astrophysics, University of Central Lancashire, Preston, PR1 2HE, United Kingdom Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany