Can gravitational infall energy lead to the observed velocity dispersion in DLAs?

The median observed velocity width v90 of low- ionization species in damped Ly systems is close to 90 km s 1, with 10% of all systems showing v90 k210 km s 1 at z 3. We show that a relative shortage of such highvelocity neutral gas absorbers in state- of- the-art galaxy formationmodels is a fundamental problem, present in both grid- based and particle- based numerical simulations. Using a series of numerical simulations of varying resolution and box size to cover a wide range of halo masses, we demonstrate that energy from gravitational infall alone is insufficient to produce the velocity dispersion observed in damped Ly systems, nor does this dispersion arise from an implementation of star formation and feedback in our highest resolution (45 pc) models, if we do not put any galactic winds into our models by hand. We argue that these numerical experiments highlight the need to separate the dynamics of different components of the multiphase interstellar medium at z 3.