Work

The youth of the intracluster medium

Year: 2026

Type: article

Abstract: Context. Protoclusters of galaxies are the earliest phase in the assembly of galaxy clusters, and they can provide invaluable information about plasma physics, cosmic magnetism, and cosmology. However, due to small angular sizes and cosmological dimming, observing the proto-intracluster medium (proto-ICM) associated with protocluster cores is far from trivial. Aims. We aim to provide a non-parametric description of the gas mass and electron number density profiles of the proto-ICM at z = 2 and to study their dependence on mass, dynamical state, and central activity. Methods. We extracted and analysed over 3800 regions around protocluster cores with spherical overdensity masses above M 500c > 10 13 M ⊙ out of a large simulated volume within the M AGNETICUM suite. We studied their density profiles, temperature structure, ionisation degree, and electron number density as a function of mass and other secondary properties characterising dynamical state and central activity extending from the central halo to the surrounding protocluster environment. Results. Protoclusters present moderate deviations from self-similarity in their density profiles and temperature structure, with a strong double- β structure especially relevant at high masses and intense accretion onto the central active galactic nuclei. Hot ionised gas is only dominant at intermediate radii ( r ≳ [0.1 − 0.5] R 500c ), where its density also correlates with mass and dynamical disturbance. Conclusions. These results constitute the basis for a forthcoming parametric calibration of proto-ICM density profiles, which could be useful for interpreting observables sensitive to the density and ionisation of the diffuse gas.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202660465

Authors: David Vallés-Pérez, Annalisa Bonafede, Klaus Dolag, Marco Balboni, Paolo Tozzi, Marika Lepore