Neutral hydrogen in galactic fountains

Simulations of an isolated Milky Way-like galaxy, in which supernovae power a galactic fountain, reproduce the observed velocity and 21 cm brightness statistics of galactic neutral hydrogen (H i). The simulated galaxy consists of a thin H i disk, similar in extent and brightness to that observed in the Milky Way, and extra-planar neutral gas at a range of velocities due to the galactic fountain. Mock observations of the neutral gas resemble the H i flux measurements from the Leiden-Argentine-Bonn (LAB) H i survey, including a high-velocity tail which matches well with observations of highvelocity clouds. The simulated high-velocity clouds are typically found close to the galactic disk, with a typical line-of-sight distance of 13 kpc from observers on the solar circle. The fountain efficiently cycles matter from the centre of the galaxy to its outskirts at a rate of around 0.5M⊙yr .