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 $20$~kpc from the host galaxy center on
infalling cold gas streams originating from the intergalactic medium, with
infall velocity of $100$ km/s and temperature of $10^4$ 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 ($n_gas \sim
10^-2$ cm$^-3$), Jeans quasi-stable, and have very low star formation rate
($\Sigma 10^-4 \ yr^-1 \ kpc^-2$). 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 ($5$ 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.
Description
[1511.07060] The Physical Nature of the Most Metal-Poor Damped Lyman Alpha Systems
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