Mathematics – Logic
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21734501n&link_type=abstract
American Astronomical Society, AAS Meeting #217, #345.01; Bulletin of the American Astronomical Society, Vol. 43, 2011
Mathematics
Logic
Scientific paper
We study the impact of ultra-violet background radiation field (UVB) and the local stellar radiation on the HI column density distribution f(NHI) of damped Lyman-alpha systems (DLAs) and sub-DLAs at z=3 using cosmological smoothed particle hydrodynamics simulations. We find that, in the previous simulations with an optically thin approximation, the UVB was sinking into the HI cloud too deeply, and therefore we underestimated the f(NHI) at 19 < log(NHI) < 21.2 compared to the observations. When the UVB is shut off in the high-density regions with ngas > 6 x 10-3 cm-3, then we reproduce the observed f(NHI) at z=3 very well. We also investigate the effect of local stellar radiation by post-processing our simulation with a radiative transfer code, and find that the local stellar radiation reduces the f(NHI) by a factor of 0.7, which further improves the agreement with the observation. Our results show that the shape of f(NHI) is determined primarily by the treatment of UVB, with a weaker effect by the local stellar radiation, and that the optically thin approximation often used in cosmological simulation is inadequate to properly treat the ionization structure of neutral gas in and out of DLAs.
Choi Jaedong
Nagamine Kentaro
Yajima Hidenobu
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