The Evolution of the Intergalactic Medium

TL;DR

This paper reviews the current understanding of the intergalactic medium (IGM), its evolution, and the key unresolved questions, emphasizing the progress made at intermediate redshifts and the challenges at lower and higher redshifts.

Contribution

It provides a comprehensive review of theoretical models and measurements of the IGM, highlighting recent successes and unresolved puzzles in the field.

Findings

Models explain Lyman-alpha absorption at 2<z<5

Unsolved puzzles include reionization and missing baryons

Progress in understanding IGM evolution and structure formation

Abstract

The bulk of cosmic matter resides in a dilute reservoir that fills the space between galaxies, the intergalactic medium (IGM). The history of this reservoir is intimately tied to the cosmic histories of structure formation, star formation, and supermassive black hole accretion. Our models for the IGM at intermediate redshifts (2<z<5) are a tremendous success, quantitatively explaining the statistics of Lyman-alpha absorption of intergalactic hydrogen. However, at both lower and higher redshifts (and around galaxies) much is still unknown about the IGM. We review the theoretical models and measurements that form the basis for the modern understanding of the IGM, and we discuss unsolved puzzles (ranging from the largely unconstrained process of reionization at high-z to the missing baryon problem at low-z), highlighting the efforts that have the potential to solve them.