The cooler past of the intracluster medium in TNG-Cluster

TL;DR

This study uses TNG-Cluster simulations to trace the evolution of cool gas in galaxy cluster atmospheres over cosmic time, revealing its origins, distribution, and relation to satellite galaxies and black hole activity.

Contribution

It provides new insights into the evolution and distribution of cool intracluster medium gas, linking it to satellite galaxies and SMBH feedback over 13 billion years.

Findings

Cool ICM mass increases with redshift at fixed cluster mass.

Cool gas at low redshift is mainly in satellite galaxies, while at high redshift it accretes from filaments.

Cool ICM mass correlates with satellite count and inversely with SMBH mass.

Abstract

The intracluster medium (ICM) today is comprised largely of hot gas with clouds of cooler gas of unknown origin and lifespan. We analyze the evolution of cool gas (temperatures $\lesssim10^{4.5}$ K) in the ICM of 352 galaxy clusters from the TNG-Cluster simulations, with present-day mass $\sim10^{14.3-15.4}\,{\rm M_\odot}$. We follow the main progenitors of these clusters over the past $\sim13$ billion years (since $z\lesssim7$) and find that, according to TNG-Cluster, the cool ICM mass increases with redshift at fixed cluster mass, implying that this cooler past of the ICM is due to more than just halo growth. The cool cluster gas at $z\lesssim0.5$ is mostly located in and around satellite galaxies, while at $z\gtrsim2$ cool gas can also accrete via filaments from the intergalactic medium. Lower-mass and higher-redshift clusters are more susceptible to cooling. The cool ICM mass correlates with the number of gaseous satellites and inversely with the central supermassive black hole (SMBH) mass. The average number of gaseous satellites decreases since $z=2$, correlating with the decline in the cool ICM mass over cosmic time, suggesting a link between the two. Concurrently, kinetic SMBH feedback shifts the ICM temperature distribution, decreasing the cool ICM mass inside-out. At $z\approx0.5$, the predicted \ion{Mg}{ii} column densities are in the ballpark of recent observations, where satellites and other halos contribute significantly to the total \ion{Mg}{ii} column density. Suggestively, a non-negligible amount of the ICM cool gas forms stars in-situ at early times, reaching $\sim10^{2}\,{\rm M_\odot}\,{\rm yr^{-1}}$ and an H$\alpha$ surface brightness of $\sim10^{-17}\,{\rm erg\,s^{-1}\,cm^{-2}\,arcsec^{-2}}$ at $z\approx2$, detectable with Euclid and JWST.