ar X iv : a st ro - p h / 05 10 72 9 v 3 1 7 Ja n 20 07 Distribution of Damped Lyman - α Absorbers in a Λ Cold Dark Matter Universe

We present the results of a numerical study of a galactic wind model and its implications on the properties of damped Lyman-α absorbers (DLAs) using cosmological hydrodynamic simulations. We vary both the wind strength and the internal parameters of the the wind model in a series of cosmological smoothed particle hydrodynamics (SPH) simulations that include radiative cooling and heating by a UV background, star formation, and feedback from supernovae and galactic winds. To test our simulations, we examine the DLA ‘rate-of-incidence’ as a function of halo mass, galaxy apparent magnitude, and impact parameter. We find that the statistical distribution of DLAs does not depend on the exact values of internal numerical parameters that control the decoupling of hydrodynamic forces when the gas is ejected from starforming regions, although the exact spatial distribution of neutral gas may vary for individual halos. The DLA rate-of-incidence in our simulations at z = 3 is dominated (80 − 90%) by the faint galaxies with apparent magnitude RAB < 25.5. However, interestingly in a ‘strong wind’ run, the differential distribution of DLA sight-lines is peaked at Mhalo = 10 12 hM⊙ (RAB ≃ 27), and the mean DLA halo mass is 〈MDLA〉 = 10 12.4 hM⊙ (RAB ≃ 26). These mass-scales are much larger than those if we ignore winds, because galactic wind feedback suppresses the DLA cross section in low-mass halos and increases the relative contribution to the DLA incidence from more massive halos. The DLAs in our simulations are more compact than the present-day disk galaxies, and the impact parameter distribution is very narrow unless we limit the search for the host galaxy to only bright Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424 Present address: Department of Physics & Astronomy, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4002 Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138, U.S.A. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85740 Garching bei München, Germany