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

TL;DR

This study uses the TNG-Cluster simulation to investigate the presence and detectability of hot circumgalactic media around massive satellite galaxies in galaxy clusters, revealing that many satellites retain hot gas detectable via X-ray emission.

Contribution

It provides the first detailed analysis of the hot CGM in satellite galaxies within massive clusters using cosmological simulations, highlighting its brightness and extent.

Findings

Most satellites retain some hot or cold gas, especially at higher stellar masses.

The hot CGM around satellites can be observed in X-ray, being significantly brighter than the background.

Satellite CGM contributes notably to the X-ray emission in cluster outskirts.

Abstract

The most massive galaxy clusters in the Universe host hundreds of massive satellite galaxies~$\mstar\sim10^{10-12.5} msun$, but it is unclear if these satellites are able to retain their own gaseous halos. We analyze the evolution of $\approx90,000$ satellites of stellar mass $\sim10^{9-12.5} msun$ around 352 galaxy clusters of mass $\mvir\sim10^{14.3-15.4} msun$ 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 $\mvirhost\sim10^{14.5} (10^{15}) msun$ hosts $\sim100 (300)$ satellites today. Only a minority of satellites retain some gas, hot or cold, and this fraction increases with stellar mass. Lower-mass satellites $\sim10^{9-10} msun$ 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 $\sim10^{10.5-12.5} msun$, 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 $\gtrsim10$~times brighter than the local background. This X-ray surface brightness excess around satellites extends to $\approx30-100$ 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 $\approx0.75-1.5\rvir$ 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.