Astronomy and Astrophysics
Aims: The primary goal of this work is to identify optimal locations of the enhanced X-ray emission and absorption, arising from the interaction of infalling filamentary gas with cluster material. Our further goal is to improve our understanding of the various physical processes affecting WHIM as it falls towards clusters of galaxies along the cosmic filaments. We aim to utilise this information for planning future X-ray observations of WHIM in cluster outskirts.
Methods: We applied the DisPerSE filament finder to the galaxy distribution in the surroundings of a single Coma-like (M200 ∼ 1015.4 M⊙) simulated C-EAGLE cluster of galaxies. We characterised the distribution of the thermodynamic properties of the gas in such filaments and provided a physical interpretation for the results. This analysis serves as a proof of method to be applied to the full C-EAGLE sample in a future work.
Results: We captured a large fraction (∼50%) of the hot (T > 105.5 K) gas falling towards the cluster in the detected filaments in the cluster outskirts. The gas in the filaments is in approximate free fall all the way down to the radial distance of ∼2 r200 from the cluster. At smaller radii, the filament gas begins to slow down due to the increasing pressure of the ambient gas; approximately half of the filament gas nevertheless penetrates into the cluster before being decelerated. The deceleration is accompanied by the conversion of gas bulk kinetic energy into heat. As a result, the density and temperature of the gas in the filaments increase from the general Cosmic Web level of ρ ∼ 10ρav (where ρav is the cosmic mean baryon density) and T = 105 − 106 K at r ∼ 4 r200 towards ρ ∼ 100ρav and T = 107 − 108 K at the virial boundary of the very massive cluster studied in this paper.
Conclusions: The detection of the cosmic filaments of galaxies around clusters may provide a practical observational avenue for locating the densest and hottest phase of the missing baryons. Movie associated to Fig. 4 is available at https://www.aanda.org.