The physical nature of the most metal-poor damped Lyman α 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 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 ∼ 10 −2 cm −3 ), Jeans quasi-stable, and have very low star formation rate (Σ 10 −4 M 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.

Discovery of a Damped Lyα System in a Low-z Galaxy Group: Possible Evidence for Gas Inflow and Nuclear Star Formation

“…of the low-redshift DLAs were believed to be associated with extended disks, the inner circumgalactic medium, or satellite galaxies (e.g. Neeleman et al 2017), while simulations showed that the high-z DLAs were not necessarily galaxy disks (Gardner et al 2001;Pontzen et al 2008;Yajima et al 2012;Cen 2012;Rahmati et al 2013;Yuan & Cen 2016).…”

Discovery of the most metal-poor damped Lyman-α system

“…The most metal-poor DLAs are thought to be the antecedents of the lowest mass galaxies (Salvadori & Ferrara 2012;Cooke, Pettini & Jorgenson 2015), as well as cold gas streams being accreted on to galaxies (Yuan & Cen 2016). Such an affiliation marks these DLAs as a promising environment to measure -at high redshift -the chemical abundance pattern of the earliest generation of stars.…”

Gas Accretion and Star Formation Rates

“…This is particularly true where the hot quasi-static halo interacts with cold rapidly-inflowing IGM accretion. Some of the resulting complications are revealed in the study of metal-poor DLAs carried out by Yuan & Cen (2016). The majority of the metal-poor DLAs are far from the central galaxy (≥ 20 kpc) and result from the cold gas streams from the IGM.…”