Lost Baryons at Low Redshift

Abstract

AbstractWe review our attempts to discover lost baryons at low redshift with the “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.