Large-Scale X-ray Studies of Nearby Galaxy Clusters with eROSITA

Abstract

Galaxy clusters form in the intersections of the cosmic web and grow through mergers and accretion of smaller substructures transported by the cosmic filaments. Hence, the outskirts of galaxy clusters are of great significance for studying the physics of accretion processes (e.g., shocks and gas motions) and for detecting the elusive cosmic filaments. The cosmic filaments host the warm-hot intergalactic medium (WHIM) and tracing them helps locate the 40% unaccounted baryons in the local Universe. Despite the importance, studying cluster outskirts was hindered by the lack of soft X-ray energy sensitivity and small field-of-views (FoVs). The SRG/eROSITA instrument, with its large FoV and superior soft X-ray sensitivity, enables detailed exploration of faint cluster outskirts and the densest parts of filaments. This dissertation employs eROSITA to investigate two cluster fields, characterizing gas properties in their outskirts and filaments. <br /> The eROSITA PV data of the A3391/95 galaxy cluster system reveals a snapshot of large-scale structure formation, revealing ~15 Mpc-long warm-hot emission connecting at least six clusters and groups. Analyses of cluster outskirts show elevated temperatures in filament-facing regions, driven by shocks from matter accretion. The detected filaments exhibit temperatures slightly above the WHIM’s predicted upper limit, likely due to enhanced gravitational heating in this dense environment. <br /> The Centaurus cluster, one of the brightest and nearest clusters, is an excellent target for studying the outskirts of galaxy clusters. Previous research focused on the inner region of the cluster, covering a radius of 30 arcmin. However, using data from the combined eROSITA all-sky survey (eRASS:5), the spectral analysis has been extended to ~90 arcmin. The results indicate that, while the core of the cluster is dynamically active, the outskirts remain largely undisturbed and show no influence from cosmic filaments.