The Physical Nature of the Most Metal-Poor Damped Lyman Alpha Systems

Abstract

Utilizing the high-resolution, large-scale LAOZI cosmological simulations we investigate the nature of the metal-poor ($[Z/H]<-2$) damped Lyman alpha systems (mpDLA) at $z=3$. The following physical picture of mpDLAs emerges. The majority of mpDLAs inhabit regions $\ge 20$~kpc from the host galaxy center on infalling cold gas streams originating from the intergalactic medium, with infall velocity of $\sim 100$ km/s and temperature of $\sim 10^4$ K. For each host galaxy, on average, about $1\%$ of the area within a radius $150$~kpc is covered by mpDLAs. The mpDLAs are relatively diffuse ($n_{\mathrm{gas}}\sim 10^{-2}$ cm${}^{-3}$), Jeans quasi-stable, and have very low star formation rate ($\dot{\Sigma }\le 10^{-4}{M}_{\odot }{\mathrm{yr}}^{-1}{\mathrm{kpc}}^{-2}$). As mpDLAs migrate inward to the galaxy center, they mix with high metallicity gas and stellar outflows in the process, removing themselves from the metal-poor category and rendering the central ($\le 5$ kpc) regions of galaxies devoid of mpDLAs. Thus, the central regions of the host galaxies are populated by mostly metal-rich DLAs instead of mpDLAs. All observables of the simulated mpDLAs are in excellent agreement with observations, except the gas density, which is about a factor of ten lower than the value inferred observationally. However, the observationally inferred value is based on simplified assumptions that are not borne out in the simulations.

13 pages, 9 figures. Published on MNRAS

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Cited by in corpus (5)

• Discovery of the most metal-poor damped Lyman-alpha system
• Gas Accretion and Star Formation Rates
• Probing the assembly of dwarf galaxies through cosmic time with damped Lyman-$\alpha$ absorption spectroscopy
• Discovery of a Damped Ly-alpha System in a Low-z Galaxy Group: Possible Evidence for Gas Inflow and Nuclear Star Formation
• A survey of extremely metal-poor gas at cosmic noon: evidence of elevated [O/Fe]