The hot circumgalactic media of massive cluster satellites in the TNG-Cluster simulation: Existence and detectability

Abstract

The most massive galaxy clusters in the Universe host tens to hundreds of massive satellite galaxies $ but it is unclear if these satellites are able to retain their own gaseous atmospheres. We analyze the evolution of $ satellites of stellar mass $ around 352 galaxy clusters of mass $ at $z=0$ from the new TNG-Cluster suite of cosmological magneto-hydrodynamical galaxy cluster simulations. The number of massive satellites per host increases with host mass, and the mass--richness relation broadly agrees with observations. A halo of mass $ hosts $ satellites today. Only a minority of satellites retain some gas, hot or cold, and this fraction increases with stellar mass. lower-mass satellites $ are more likely to retain part of their cold interstellar medium, consistent with ram pressure preferentially removing hot extended gas first. At higher stellar masses $ the fraction of gas-rich satellites increases to unity, and nearly all satellites retain a sizeable portion of their hot, spatially extended circumgalactic medium (CGM), despite the ejective activity of their supermassive black holes. According to TNG-Cluster, the CGM of these gaseous satellites can be seen in soft X-ray emission (0.5-2.0 keV) that is,$ times brighter than the local background. This X-ray surface brightness excess around satellites extends to $ kpc, and is strongest for galaxies with higher stellar masses and larger host-centric distances. Approximately $10$ percent of the soft X-ray emission in cluster outskirts $ originates from satellites. The CGM of member galaxies reflects the dynamics of cluster-satellite interactions and contributes to the observationally inferred properties of the intracluster medium.