GSH 006-15+7: a local Galactic supershell featuring transition from H i emission to absorption

Abstract

We report on the discovery of a new Galactic supershell, GSH 006−15+7, from the Galactic All Sky Survey data. Observed and derived properties are presented and we find that GSH 006−15+7 is one of the nearest physically large supershells known, with dimensions of ∼ 780 × 520 pc at a distance of ∼ 1.5 kpc. The shell wall appears in Hi emission at b . −6.5 ◦ and in Hi self-absorption (HiSA) at b & −6.5 ◦. We use this feature along with HiSA diagnostics to estimate an optical depth of τ ∼ 3, a spin temperature of ∼ 40 K and a swept-up mass of M ∼ 3 × 106 M⊙. We also investigate the origin of GSH 006−15+7, assessing the energy contribution of candidate powering sources and finding evidence in favour of a formation energy of ∼ 1052 ergs. We find that this structure provides evidence for the transfer of mass and energy from the Galactic disk into the halo.