The 'Carina Flare' supershell: probing the atomic and molecular ISM in a Galactic chimney

The 'Carina Flare' supershell, GSH 287+04?17, is a molecular supershell originally discovered in  ¹²CO( J = 1–0)  with the NANTEN 4 m telescope. We present the first study of the shell's atomic ISM, using H  i 21-cm line data from the Parkes 64-m telescope Southern Galactic Plane Survey. The data reveal a gently expanding,  ～230 × 360  pc H  i supershell that shows strong evidence of Galactic Plane blowout, with a break in its main body at   z ～ 280  pc and a capped high-latitude extension reaching   z ～ 450  pc. The molecular clouds form comoving parts of the atomic shell, and the morphology of the two phases reflects the supershell's influence on the structure of the ISM. We also report the first discovery of an ionized component of the supershell, in the form of delicate, streamer-like filaments aligned with the proposed direction of blowout. The distance estimate to the shell is re-examined, and we find strong evidence to support the original suggestion that it is located in the Carina Arm at a distance of  2.6 ± 0.4 kpc  . Associated H  i and H₂ masses are estimated as   M _H I≈ 7 ± 3 × 10⁵ M_⊙  and     , and the kinetic energy of the expanding shell as   E _K ～ 1 × 10⁵¹  erg. We examine the results of analytical and numerical models to estimate a required formation energy of several 10⁵¹ to  ～10⁵²  erg, and an age of  ～10⁷ yr  . This age is compatible with molecular cloud formation time-scales, and we briefly consider the viability of a supershell-triggered origin for the molecular component.