Gas accretion onto galaxies and Kelvin-Helmholtz turbulence

Abstract

Continued star formation over the lifetime of a galaxy suggests that low metalicity gas is steadily flowing in from the circumgalactic medium. Also, cosmological simulations of large-scale structure formation imply that gas is accreted onto galaxies from the halo inside which they formed. Direct observations are difficult, but in recent years observational indications of gas inflows from a circumgalactic medium were obtained. Here we suggest an indirect observational probe: looking for large-scale (exceeding few kpc) turbulence caused by the accretion. As a specific example we consider an accretion flow coplanar with the galaxy disk, and argue that Kelvin-Helmholtz turbulence will be generated. We employ a semi-analytic model of turbulence and derive the expected turbulence power spectrum. The latter turns out to be of a distinctive shape that can be compared with observational power spectra. As an illustrative example we use parameters of the Milky Way galaxy.