Exploring Cloudy Gas Accretion as a Source of Interstellar Turbulence in the Outskirts of Disks

Abstract

High-resolution two-dimensional MHD numerical simulations have been carried out to investigate the effects of the continuing infall of clumpy gas in extended H I galactic disks. Given a certain accretion rate, the response of the disk depends on its surface gas density and temperature. For Galactic conditions at a galactocentric distance of ~20 kpc, and for mass accretion rates consistent with current empirical and theoretical determinations in the Milky Way, the rain of compact high-velocity clouds onto the disk can maintain transonic turbulent motions in the warm phase (~2500 K) of H I. Hence, the H I line width is expected to be ~6.5 km s-1 for a gas layer at 2500 K, if infall is the only mechanism driving the turbulence. Some statistical properties of the resulting force flow are shown in this Letter. The radial dependence of the gas velocity dispersion is also discussed.