Lost Baryons at Low Redshift

TL;DR

This paper reviews efforts to detect the missing baryons at low redshift through X-ray absorption lines, highlighting current evidence, debates, and future prospects with advanced X-ray observatories.

Contribution

It synthesizes existing observations and discusses the potential of upcoming X-ray missions to map the warm-hot intergalactic medium and locate lost baryons.

Findings

Evidence along the Mrk 421 sightline supports the presence of warm-hot intergalactic medium.

The debate over the origin of z=0 absorption systems remains unresolved, likely involving both Galactic and extragalactic components.

Next-generation X-ray missions are essential for advancing the understanding of low-redshift baryons.

Abstract

We review our attempts to discover lost baryons at low redshift with ``X-ray forest'' of absorption lines from the warm-hot intergalactic medium. We discuss the best evidence to date along the Mrk 421 sightline. We then discuss the missing baryons in the Local Group and the significance of the z=0 absorption systems in X-ray spectra. We argue that the debate over the Galactic vs. extragalactic origin of the z=0 systems is premature as these systems likely contain both components. Observations with next generation X-ray missions such as Constellation-X and XEUS will be crucial to map out the warm-hot intergalactic medium.