Gas around galaxy haloes - II: hydrogen absorption signatures from the environments of galaxies at redshifts 2 < z < 3

TL;DR

This study compares cosmological hydrodynamical simulation predictions with observations of neutral hydrogen absorption around galaxy haloes at redshifts 2-3, identifying different gaseous regions and their contributions to absorption signatures.

Contribution

It provides a detailed analysis of hydrogen absorption signatures around galaxy haloes, highlighting the roles of various physical processes and the robustness of predictions across different simulation methods.

Findings

Robust predictions for mesogalactic and intergalactic absorption agree with observations.

Star formation and wind feedback are secondary outside the virial radius.

Simulating the virialized region's absorption requires higher resolution or additional physics.

Abstract

We compare predictions of large-scale cosmological hydrodynamical simulations for neutral hydrogen absorption signatures in the vicinity of 1e11 - 1e12.5 MSun haloes with observational measurements. Two different hydrodynamical techniques and a variety of prescriptions for gas removal in high density regions are examined. Star formation and wind feedback play only secondary roles in the HI absorption signatures outside the virial radius, but play important roles within. Accordingly, we identify three distinct gaseous regions around a halo: the virialized region, the mesogalactic medium outside the virial radius arising from the extended haloes of galaxies out to about two turnaround radii, and the intergalactic medium beyond. Predictions for the amount of absorption from the mesogalactic and intergalactic media are robust across different methodologies, and the predictions agree with the amount of absorption observed around star-forming galaxies and QSO host galaxies. Recovering the measured amount of absorption within the virialized region, however, requires either a higher dynamic range in the simulations, additional physics, or both.