We use high resolution Eulerian hydrodynamics simulations to study kinematic properties of the low ionization species in damped Ly \alpha systems at redshift z = 3 .
Our adaptive mesh refinement simulations include most key ingredients relevant for modeling neutral gas in high-column density absorbers : hydrodynamics , gravitational collapse , continuum radiative transfer above the hydrogen Lyman limit and gas chemistry , but no star formation .
We model high-resolution Keck spectra with unsaturated low ion transitions in two Si II lines ( 1526 and 1808 { A } ) , and compare simulated line profiles to the data from the SDSS DLA survey .

We find that with increasing grid resolution the models show a trend in convergence towards the observed distribution of HI column densities .
While in our highest resolution model we recover the cumulative number of DLAs per unit absorption distance , none of our models predicts DLA velocity widths as high as indicated by the data , suggesting that feedback from star formation might be important .
At z = 3 a non-negligible fraction of DLAs with column densities below 10 ^ { 21 } { cm } ^ { -2 } is caused by filamentary structures in more massive halo environments .
Lower column density absorbers with N _ { HI } < 10 ^ { 21.4 } { cm } ^ { -2 } are sensitive to changes in the UV background resulting in a 10 \% reduction of the cumulative number of DLAs for twice the quasar background relative to the fiducial value , and nearly a 40 \% reduction for four times the quasar background .
We find that the mass cut-off below which a large fraction of dwarf galaxies can not retain gas after reionization is \sim 7 \times 10 ^ { 7 } { M _ { \odot } } , lower than the previous estimates .
Finally , we show that models with self-shielding commonly used in the literature produce significantly lower DLA velocity widths than the full radiative transfer runs which essentially render these self-shielded models obsolete .