2016MNRAS.457..487Y

Utilizing the high-resolution, large-scale LAOZI cosmological simulations we investigate the nature of the metal-poor ([Z/H] < -2) damped Lyman α systems (mpDLA) at z = 3. The following physical picture of mpDLAs emerges. The majority of mpDLAs inhabit regions >=20 kpc from the host galaxy centre on infalling cold gas streams originating from the intergalactic medium, with infall velocity of ∼100 km /s and temperature of ∼10⁴ K. For each host galaxy, on average, about 1 per cent of the area within a radius 150 kpc is covered by mpDLAs. The mpDLAs are relatively diffuse (ngas ∼ 10^–2 cm^–3), Jeans quasi-stable, and have very low star formation rate (). As mpDLAs migrate inwards to the galaxy centre, they mix with high-metallicity gas and stellar outflows in the process, removing themselves from the metal-poor category and rendering the central (<=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 10 lower than the value inferred observationally. However, the observationally inferred value is based on simplified assumptions that are not borne out in the simulations.