EFFECTS OF ULTRAVIOLET BACKGROUND AND LOCAL STELLAR RADIATION ON THE H I COLUMN DENSITY DISTRIBUTION
- Department of Physics and Astronomy, University of Nevada Las Vegas, 4505 Maryland Pkwy, Box 454002, Las Vegas, NV 89154-4002 (United States)
- Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)
We study the impact of ultraviolet background (UVB) radiation field and the local stellar radiation on the H I column density distribution f(N{sub H{sub I}}) of damped Ly{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 H I cloud too deeply, and therefore we underestimated the f(N{sub H{sub I}}) at 19 < log N{sub H{sub I}} < 21.2 compared to the observations. If the UVB is shut off in the high-density regions with n{sub gas}>6 x 10{sup -3} cm{sup -3}, then we reproduce the observed f(N{sub H{sub I}}) at z = 3 very well. We also investigate the effect of local stellar radiation by postprocessing our simulation with a radiative transfer code and find that the local stellar radiation does not change the f(N{sub H{sub I}}) very much. Our results show that the shape of f(N{sub H{sub I}}) is determined primarily by the UVB with a much 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. Our result also indicates that the DLA gas is closely related to the transition region from optically thick neutral gas to optically thin ionized gas within dark matter halos.
- OSTI ID:
- 21454873
- Journal Information:
- Astrophysical Journal Letters, Vol. 725, Issue 2; Other Information: DOI: 10.1088/2041-8205/725/2/L219; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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