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

The most massive galaxy clusters in the Universe host hundreds of massive satellite galaxies ∼10^10-12.5 msun, but it is unclear if these satellites are able to retain their own gaseous halos. We analyze the evolution of ≈90,000 satellites of stellar mass ∼10^9-12.5 msun around 352 galaxy clusters of mass ∼10^14.3-15.4 msun 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 ∼10^14.5 (10^15) msun hosts ∼100 (300) satellites today. Only a minority of satellites retain some gas, hot or cold, and this fraction increases with stellar mass. Lower-mass satellites ∼10^9-10 msun 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 ∼10^10.5-12.5 msun, the fraction of gas-rich satellites increases to unity, and nearly all satellites retain a 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 ≳10 times brighter than the local background. This X-ray surface brightness excess around satellites extends to ≈30-100 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 ≈0.75-1.5 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.