The Intergalactic Medium
Abstract
The intergalactic medium (IGM) comprises all the matter that lies between galaxies. Hosting the vast majority () of the baryons in the Universe, the IGM is a critical reservoir and probe for cosmology and astrophysics, providing insights into large-scale structure formation and galaxy evolution. In this Chapter, we present an overview of the general properties of the IGM, focusing on their dependence on cosmic environment and cosmic time. Emphasis is given to the basic physical principles that allow us to model the density, temperature, and ionization state of the IGM, supported by results from cosmological hydrodynamical simulations. We also cover the foundational principles of quasar spectroscopy used to probe the IGM in absorption, with a particular focus on HI absorption lines. Finally, we briefly discuss future prospects and complementary observational techniques to enhance our understanding of the IGM.
Keywords
Cite
@article{arxiv.2504.12539,
title = {The Intergalactic Medium},
author = {Nicolas Tejos},
journal= {arXiv preprint arXiv:2504.12539},
year = {2025}
}
Comments
This is a pre-print of a chapter for the Encyclopedia of Astrophysics (edited by I. Mandel, section editor S. McGee) to be published by Elsevier as a Reference Module; 32 pages, 10 figures