IAU00561
Presentation type requested: ORAL
DAMPED LYMAN-ALPHA ABSORBERS IN COSMOLOGICAL SPH SIMULATIONS
Kentaro Nagamine
Harvard-Smithsonian Center for Astrophysics
We use cosmological smoothed-particle hydrodynamics (SPH) simulations of the Lambda-CDM model to study the abundance of damped Lyman-alpha absorbers in the redshift range z=0-4.5. Our approach includes a phenomenological model of galactic wind. We show that the DLA abundance was overestimated in previous studies for three reasons: (1) the overcooling of gas occurring with non-conservative formulations of SPH, (2) a lack of numerical resolution, and (3) an inadequate treatment of feedback. Our new results for the total neutral hydrogen mass density, DLA abundance, and column density distribution function all agree reasonably well with observational estimates at z=3, indicating that DLAs arise naturally from radiatively cooled gas in dark matter haloes that form in a Lambda-CDM universe. Our simulations suggest a moderate decrease in DLA abundance by roughly a factor of two from z=4.5 to 3, consistent with observations. A significant decline in abundance from z=3 to z=1, followed by weak evolution from z=1 to z=0, is also indicated, but our low-redshift results need to be interpreted with caution because of the coarser resolution. Our highest resolution simulation also suggests that the halo mass-scale below which DLAs do not exist is slightly above 10^8 Msun/h at z=3-4.
Springel Volker , Hernquist Lars
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