English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We study the impact of ultraviolet background (UVB) radiation field and thelocal stellar radiation on the H_I column density distribution f(N_HI) ofdamped Ly-alpha systems (DLAs) and sub-DLAs at z=3 using cosmological smoothedparticle hydrodynamics simulations. We find that, in the previous simulationswith an optically thin approximation, the UVB was sinking into the H_I cloudtoo deeply, and therefore we underestimated the f(N_HI) at 19 < log(N_HI) <21.2 compared to the observations. If the UVB is shut off in the high-densityregions with n_gas > 6 x 10^{-3} cm^{-3}, then we reproduce the observedf(N_HI) at z=3 very well. We also investigate the effect of local stellarradiation by post-processing our simulation with a radiative transfer code, andfind that the local stellar radiation does not change the f(N_HI) very much.Our results show that the shape of f(N_HI) is determined primarily by the UVBwith a much weaker effect by the local stellar radiation and that the opticallythin approximation often used in cosmological simulation is inadequate toproperly treat the ionization structure of neutral gas in and out of DLAs. Ourresult also indicates that the DLA gas is closely related to the transitionregion from optically-thick neutral gas to optically-thin ionized gas withindark matter halos.

Effects of Ultraviolet Background and Local Stellar Radiation on the H_I Column Density Distribution