Entropy plateaus can emerge from gas replacement at a characteristic halo mass in simulated groups and clusters of galaxies

Altamura, E ORCID: 0000-0001-6973-1897, Kay, ST ORCID: 0000-0002-2277-9049, Schaye, J ORCID: 0000-0002-0668-5560, McCarthy, IG ORCID: 0000-0002-1286-483X and Schaller, M ORCID: 0000-0002-2395-4902 (2025) Entropy plateaus can emerge from gas replacement at a characteristic halo mass in simulated groups and clusters of galaxies. Monthly Notices of the Royal Astronomical Society, 541 (4). pp. 3367-3387. ISSN 0035-8711

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Abstract

The evolution of the intergalactic medium (IGM) isinfluenced by gravitational collapse, radiative cooling, and baryonic feedback. Using cosmological hydrodynamic zoom-in simulations of a 8.83 × 1012 M⊙ group and a 2.92 × 1014 M⊙ cluster at z = 0, we investigate the emergence of entropy plateaus and their connection to feedback mechanisms. This set-up uses the SWIFT-EAGLE model with three resolutions, down to an initial particle gas mass of 2.29 × 105 and 1.23 × 106 M⊙ for dark matter. We find that, when haloes reach the characteristic mass of ∼ 1012 M⊙, their entropy profiles flatten at the virial radius, marking a transition from supernova to active galactic nucleus (AGN) feedback-driven regulation. As haloes grow into groups (∼ 1013 M⊙), the entropy plateau extends inward and isentropic cores form in massive systems (∼ 1014 M⊙). By tracking the Lagrangian history of gas particles, we demonstrate that this entropy buildup is primarily driven by AGN feedback, which efficiently removes low-entropy gas from progenitors of groups and clusters, redistributing it throughout the IGM before falling into the core. Recent observations of X-GAP groups reveal large entropy excesses and plateaus, in line with our findings and in contrast to the power-law-like profiles of most previous observations. While entropy plateaus and large entropy excesses may be observationally confirmed in unbiased samples, reproducing the full diversity of entropy profiles remains an outstanding challenge for next-generation feedback models. Our results suggest that current feedback models may be overly efficient in expelling low-entropy gas from the potential cool-core progenitors, disrupting the balance between heating and cooling required for long-lived cool cores.

Item Type:	Article
Uncontrolled Keywords:	galaxies: clusters: general; galaxies: clusters: intracluster medium; galaxies: evolution; galaxies: formation; galaxies: fundamental parameters; galaxies: groups: general; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	3 July 2025
Date of first compliant Open Access:	17 April 2026
Date Deposited:	17 Apr 2026 15:00
Last Modified:	17 Apr 2026 15:00
DOI or ID number:	10.1093/mnras/staf1106
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28397

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