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




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≲−6bsl000645 and in Hi self-absorption (HiSA) at b≳−6bsl000645. 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 erg. We find that this structure provides evidence for the transfer of mass and energy from the Galactic disc into the halo.