Joint Astrophysical Colloquium
A CLEVeR view on “halo baryonification”: from galaxy groups to massive clusters
Paola Popesso (ESO)
Thursday 30/10/2025 @ 11:30, Sala Antonio Sollima (IV piano Battiferro)
Understanding the baryonification of haloes — the redistribution of baryons between galaxies, hot gas, and diffuse stellar components — is a fundamental step in modern astrophysics. While dark matter defines the gravitational potential of haloes, it is the baryons that govern observable processes such as star formation, quenching, AGN feedback, and chemical enrichment. Yet, there is substantial uncertainty in both the measured and predicted fractions of baryons in different phases, particularly at the group mass scale, where feedback processes are most efficient and diffuse components are hardest to detect. In this context, I present new results from the CLEVeR project (Cluster and groups Environment as viewed by eROSITA), based on the exploitation of eROSITA X-ray data combined with deep optical spectroscopic surveys. Using a robust stacking technique, validated against simulated data, we trace the distribution of hot gas, stellar mass, and dark matter across haloes spanning from Milky Way-sized groups to the most massive galaxy clusters. Our analysis delivers the most stringent observational constraints to date on key scaling relations — including X-ray luminosity, gas temperature, and central galaxy stellar mass versus halo mass — and enables direct measurements of hot gas and total baryon fractions over three decades in halo mass. These results challenge prevailing models of CGM–ICM thermodynamics and AGN feedback, highlighting the need to account not only for the energy budget of feedback processes, but also for their timing, spatial distribution, and halo mass dependence. The CLEVeR project provides a critical empirical benchmark to test and refine theoretical models of galaxy formation and the co-evolution of baryons and large-scale structure.