Galaxy Proximate Damped Lyman-Alpha Systems and HI Reionization Topology in TECHNICOLOR DAWN

TL;DR

This study uses cosmological simulations to assess whether proximate damped Lyman-alpha systems can effectively trace the reionization history of the universe by analyzing their relation to halo mass and ionization topology.

Contribution

It demonstrates that PDLAs, with accurate halo or stellar mass estimates, can serve as indicators of reionization progress at high redshifts, based on simulation insights.

Findings

Reionization proceeds inside-out, with the CGM reionizing after the IGM.

Neutral hydrogen column density depends mainly on halo mass.

PDLAs can trace reionization if halo or stellar mass is well estimated.

Abstract

Recent observations from the James Webb Space Telescope (JWST) have revealed proximate damped Lyman-$\alpha$ systems (PDLAs) in the foreground of high redshift galaxies ($z \gt 5$), which have been interpreted as neutral circumgalactic media (CGM). The ionization state of the CGM, potentially inferred from DLA strength, may serve as a probe to trace the progress of reionization, similarly to the ionization state of the intergalactic medium (IGM). To determine if this method has merit, we use the cosmological hydrodynamical simulation TECHNICOLOR DAWN to study simulated gas halos at redshifts $z = 10, 8, 6,$ and $5.5$. We investigate the reionization topology to determine whether the CGM and IGM have similar ionization histories, and we study the relation between column density of neutral hydrogen (observationally measured by DLA strength), neutral fraction, and gas mass fraction of the foreground gas to determine whether PDLAs can be used to trace the progress of reionization. We find an inside-out-middle reionization topology, where the CGM reionizes after the IGM and remains partially neutral at $ z= 5.5$. The foreground column density of neutral hydrogen depends mostly on halo mass, with a weak dependence on neutral fraction or redshift. Therefore, provided precise estimates of halo or stellar mass, PDLAs may be used to trace the progress of reionization particularly at high redshifts.