Mushroom-shaped structures as tracers of buoyant flow in the galactic disk

Recent H I emission observations of the southern Galactic hemisphere have r evealed a mushroom-like structure extending from z = -70 to -450 pc, compos ed of a stem and a cap. Similar structures occur in three-dimensional simul ations of a dynamic galactic disk driven by isolated and clustered supernov ae. Using these simulations, we show that hot gas in the Galactic disk that is not evacuated through chimneys expands into the cooler gas of the thick disk, forming mushroom-shaped structures. This new class of objects traces buoyant flow of hot gas into the thick disk.