Soft X-ray and extreme ultraviolet excess emission from clusters of galaxies

TL;DR

This paper reviews the detection of excess soft X-ray and extreme ultraviolet emission in galaxy clusters, discussing observational challenges and potential thermal and non-thermal origins of this phenomenon.

Contribution

It provides a comprehensive review of satellite observations and instrumental issues related to the soft excess in galaxy clusters, highlighting the ongoing controversy and possible emission mechanisms.

Findings

Detection of soft X-ray excess in multiple galaxy clusters

Instrumental issues influence the interpretation of the excess

Possible thermal and non-thermal origins discussed

Abstract

An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal emission from the hot intracluster medium has been detected in a number of clusters of galaxies. We briefly present each of the satellites (EUVE, ROSAT PSPC and BeppoSAX, and presently XMM-Newton, Chandra and Suzaku) and their corresponding instrumental issues, which are responsible for the fact that this soft excess remains controversial in a number of cases. We then review the evidence for this soft X-ray excess and discuss the possible mechanisms (thermal and non-thermal) which could be responsible for this emission.