The Host Halos of OI Absorbers in the Reionization Epoch

TL;DR

This study uses radiation hydrodynamic simulations to investigate OI absorbers during the reionization epoch, revealing their association with small dark matter halos and their potential to probe the ionizing sources more directly.

Contribution

It provides the first detailed simulation-based analysis of OI absorbers at high redshift, linking absorber properties to halo mass and reionization processes.

Findings

OI absorbers are mainly within dark matter halos at z~6.

Reionization removes gas from halos less massive than 10^8.4 M_sun.

OI absorption probes smaller halos than Lyman break galaxies.

Abstract

We use a radiation hydrodynamic simulation of the hydrogen reionization epoch to study OI absorbers at z~6. The intergalactic medium (IGM) is reionized before it is enriched, hence OI absorption originates within dark matter halos. The predicted abundance of OI absorbers is in reasonable agreement with observations. At z=10, roughly 70% of sightlines through atomically-cooled halos encounter a visible (N_OI > 10^14 cm^-2) column. Reionization ionizes and removes gas from halos less massive than 10^8.4 M_0, but 20% of sightlines through more massive halos encounter visible columns even at z=5. The mass scale of absorber host halos is 10-100 times smaller than the halos of Lyman break galaxies and Lyman-alpha emitters, hence absorption probes the dominant ionizing sources more directly. OI absorbers have neutral hydrogen columns of 10^19-10^21 cm^-2, suggesting a close resemblance between objects selected in OI and HI absorption. Finally, the absorption in the foreground of the z=7.085 quasar ULASJ1120+0641 cannot originate in a dark matter halo because halo gas at the observed HI column density is enriched enough to violate the upper limits on the OI column. By contrast, gas at less than one third the cosmic mean density satisfies the constraints. Hence the foreground absorption likely originates in the IGM.