The Gas Accretion History of Low Mass Halos within the Cosmic Web from Cosmological Simulations

TL;DR

This study uses cosmological simulations to analyze how low mass halos in the cosmic web acquire and lose gas over cosmic time, highlighting the impact of reionization and halo environment on their gas accretion and star formation history.

Contribution

It provides detailed insights into the gas accretion and loss processes of low mass halos, emphasizing the effects of reionization and local environment, which were less understood before.

Findings

Low mass halos rapidly accrete gas before reionization.

Reionization causes significant gas loss, halting star formation in the smallest halos.

More massive halos can recover and re-accrete ionized gas, especially near cosmic web structures.

Abstract

Using high resolution hydrodynamical cosmological simulations, we study the gas accretion history of low mass halos located in a field-like, low density environment. We track their evolution individually from the early, pre-reionization era, through reionization, and beyond until $z=0$. Before reionization, low mass halos accrete cool cosmic web gas at a very rapid rate, often reaching the highest gas mass they will ever have. But when reionization occurs, we see that almost all halos lose significant quantities of their gas content, although some respond less quickly than others. We find that the response rate is influenced by halo mass first, and secondarily by their internal gas density at the epoch of reionization. Reionization also fully ionises the cosmic web gas by z$\sim$6. As a result, the lowest mass halos (M$\sim$10$^6~h^{-1}$M$_\odot$ at $z=6$) can never again re-accrete gas from the cosmic web, and by $z\sim5$ have lost all their internal gas to ionisation, resulting in a halt in star formation at this epoch. However, more massive halos can recover from their gas mass loss, and re-accrete ionised cosmic web gas. We find the efficiency of this re-accretion is a function of halo mass first, followed by local surrounding gas density. Halos that are closer to the cosmic web structure can accrete denser gas more rapidly. We find that our lower mass halos have a sweet spot for rapid, dense gas accretion at distances of roughly 1-5 virial radii from the most massive halos in our sample ($>$10$^8~h^{-1}$M$_\odot$), as these tend to be embedded deeply within the cosmic web.