Cloudy intergalactic accretion flows in the outer discs of galaxies

High-resolution two-dimensional magnetohydrodynamical simulations have been carried out to investigate the role of continuing infall of clumpy gas as a driver of turbulence in extended H i galactic discs. We have compared the responses of isothermal gas discs with sound speeds 4 and 8 km/s to infalling, condensed clouds. For mass accretion rates of ∼0.6M⊙ yr−1, the turbulent motions in the outer disc become slightly faster than transonic. We suggest that the rain of compact high velocity clouds on the disc not only can fuel the Milky Way with fresh material but is a potential source of random motions in outer regions of H i discs.