Understanding entropy in massive halos: The role of baryon decoupling

Aims. The goal of the work presented in this paper is to use observed entropy profiles to infer constraints on the accretion process in massive halos. Methods. We compare entropy profiles from various observational samples with those generated by an updated version of the semi-analytical models developed in the early 2000s, that have been modified to reflect recent advancements in our understanding of large-structure formation. Results. Our model reproduces the growing departure from self-similarity observed in data when moving inward in individual profiles and down in mass across different profiles. These deviations stem from a phase of extremely low gas content centered around 10 13 M ⊙ . According to our model, halos at this mass scale are missing between 50% and 90% of their baryons, corresponding to a gas fraction ranging between 2% and 8%. Conclusions. Baryon decoupling, the mechanism at the heart of our model, proves effective in explaining much of the behavior we sought to understand.