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Description
Galaxy clusters form in the intersections of the cosmic web and grow through mergers and accretion of smaller substructures transported by the cosmic web filaments. Hence, the outskirts of galaxy clusters are important for studying the signatures of the accretion processes and detecting the elusive cosmic filaments, which are the key to solving the ”missing” baryons problem.
Despite its importance, studying these regions is hindered by the lack of soft X-ray energy sensitivity and the FoV of previous X-ray instruments. Equipped with a large FoV and survey observation mode, as well as superior soft energy band sensitivity, eROSITA is an excellent instrument to target the faint cluster outskirts and the densest parts of the filaments. Using eROSITA data, we examined the outer regions of nearby galaxy clusters, namely the Abell 3391/95 cluster system and the Centaurus cluster. We analyzed the gas properties in the cluster outskirts and the detected filaments.
We found no hint of a large-scale structure connected to the Centaurus cluster. The cluster outskirts temperature of the cluster follows the temperature profile of clusters in simulations, as well as temperature fit from other cluster outskirts measurements, which might be related to the lack of connectivity. With the eROSITA PV data of the A3391/95 system, Reiprich et al. (2021) discovered about 15 Mpc continuous warm-hot emission connecting at least five galaxy clusters and groups in the field.
In this work, we found that the filament-facing cluster outskirts are hotter than the predicted values. Furthermore, we characterized the A3391/95 filaments and found that their gas densities are within the expected WHIM range, while their temperatures are slightly hotter than the predicted WHIM temperature range. The acquired temperatures for these filaments are ∼1 keV, close to the upper WHIM range of 0.9 keV. Gravitational heating may enhance the temperature of these short filaments.
