The eventful life journey of galaxy clusters

II. Impact of mass accretion on the thermodynamic structure of the ICM

¹ Dipartimento di Fisica e Astronomia, Università di Bologna Via Piero Gobetti 93/2 IT-40129 Bologna, Italy
² Departament d’Astronomia i Astrofísica, Universitat de València ES-46100 Burjassot València, Spain
³ Observatori Astronòmic, Universitat de València ES-46980 Paterna València, Spain

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 30 September 2025
Accepted: 9 December 2025

Abstract

Context. The internal structure of the intracluster medium (ICM) is tightly linked to the assembly history and physical processes in groups and clusters, but the role of recent accretion in shaping these profiles has not been fully explored.

Aims. We investigate the extent to which mass accretion accounts for variations in ICM density and thermodynamic profiles, and what present-day structures reveal about their formation histories.

Methods. We analyse a hydrodynamical cosmological simulation including gas cooling without feedback, to isolate the effects of heating from structure formation. Median profiles of ICM quantities are introduced as a robust description of the bulk ICM. We then examine correlations between mass accretion rates or assembly indicators with temperature, entropy, pressure, gas, and dark-matter density profiles, in addition to their scatter.

Results. Accretion in the last dynamical time strongly lowers central gas densities, while leaving dark matter largely unaffected, producing a distinct signature in the baryon depletion function. Pressure and entropy show the clearest dependence on accretion, whereas temperature is less sensitive. The radii of steepest entropy, temperature, and pressure shift inwards by ∼(10 − 20)% between high- and low-accretion subsamples. Assembly-state indicators are also related to the location of these features, and accretion correlates with the parameters of common fitting functions for density, pressure, and entropy.

Conclusions. Recent accretion leaves measurable imprints on the ICM structure, highlighting the potential of thermodynamic profiles as diagnostics of cluster growth history.