Cluster outskirts and their connection to the cosmic web

TL;DR

This paper reviews recent X-ray observations and theories about galaxy cluster outskirts, their thermodynamics, chemical enrichment, and connection to the cosmic web, highlighting observational challenges and future prospects.

Contribution

It synthesizes current understanding of cluster outskirts, emphasizing the role of gas clumping, non-thermal pressure, and merging activity in shaping these regions.

Findings

Thermodynamic profiles of cluster outskirts are characterized.

Gas clumping biases affect measurements.

Future X-ray missions will probe further into cluster outskirts.

Abstract

We review the latest developments in our X-ray observational and theoretical understanding of the outskirts of galaxy clusters, and their connection to the cosmic web. The faint cluster outskirts are challenging regions to observe in X-rays, requiring highly sensitive telescopes with low and stable background levels. We present our latest understanding of the thermodynamic profiles of clusters in the outskirts, and the biases that gas clumping and non-thermal pressure support can introduce. Features in the outskirts due to merging activity are discussed, along with the chemical enrichment of the outskirts ICM. We describe future prospects for X-ray observations to explore further out in the cluster outskirts and probe their connections to the cosmic web.