Investigating the Physics and Environment of Lyman Limit Systems in Cosmological Simulations

Abstract

In this work, I investigate the properties of Lyman limit systems (LLSs) using state-of-the-art zoom-in cosmological galaxy formation simulations with on the fly radiative transfer, which includes both the cosmic UV background (UVB) and local stellar sources. I compare the simulation results to observations of the incidence frequency of LLSs and the HI column density distribution function over the redshift range $z=2-5$ and find good agreement. I explore the connection between LLSs and their host halos and find that LLSs reside in halos with a wide range of halo masses with a nearly constant covering fraction within a virial radius. Over the range $z=2-5$, I find that more than half of the LLSs reside in halos with $M<10^{10}{h}^{-1}{M}_{\odot }$, indicating that absorption line studies of LLSs can probe these low-mass galaxies which H${}_2$-based star formation models predict to have very little star formation. I study the physical state of individual LLSs and test a simple model (Schaye 2001) which encapsulates many of their properties. I confirm that LLSs have a characteristic absorption length given by the Jeans length and that they are in photoionization equilibrium at low column densities. Finally, I investigate the self-shielding of LLSs to the UVB and explore how the non-sphericity of LLSs affects the photoionization rate at a given $N_{\mathrm{HI}}$. I find that at $z\approx 3$, LLSs have an optical depth of unity at a column density of $\sim 10^{18}{\mathrm{cm}}^{-2}$ and that this is the column density which characterizes the onset of self-shielding.

13 pages, 15 figures. Updated to version accepted in MNRAS

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Cited by in corpus (6)

• The distribution of neutral hydrogen around high-redshift galaxies and quasars in the EAGLE simulation
• The Effects of Lyman-Limit Systems on the Evolution and Observability of the Epoch of Reionization
• The mean free path of hydrogen ionizing photons during the epoch of reionization
• Observed Faraday Effects in Damped Lyman-Alpha Absorbers and Lyman Limit Systems: The Magnetised Environment of Galactic Building Blocks at Redshift=2
• Discovery of a Damped Ly-alpha System in a Low-z Galaxy Group: Possible Evidence for Gas Inflow and Nuclear Star Formation
• Cosmic Reionization On Computers: Statistics, Physical Properties and Environment of Lyman Limit Systems at $z\sim 6$