The physical nature of the most metal-poor damped Lyman α systems. Issue 1 (20th January 2016)

• Record Type: Journal Article
• Authors: Yuan, Sihan; Cen, Renyue
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 457:Issue 1(2016)
• Page Start: 487
• Page End: 495
• Publication Date: 2016-01-20
• Subjects: methods: numerical -- Galaxy: formation -- Galaxy: evolution; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stv2841
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: 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 −1 and temperature of ∼10 4 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 ( n gas ∼ 10 −2 cm −3 ), Jeans quasi-stable, and have very low star formation rate ($\dot{\Sigma } \le 10^{-4} {\rm \, M_{\odot }}\rm {\ yr}^{-1} \rm {\ kpc}^{-2}$ ). 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.