Implications of feedback solutions to the S8 tension for the baryon fractions of galaxy groups and clusters

Salcido, J ORCID: 0000-0002-8918-5229 and McCarthy, IG ORCID: 0000-0002-1286-483X (2025) Implications of feedback solutions to the S8 tension for the baryon fractions of galaxy groups and clusters. Monthly Notices of the Royal Astronomical Society, 541 (2). pp. 899-910. ISSN 0035-8711

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Abstract

Recent large-scale structure (LSS) surveys have revealed a persistent tension in the value of S8 = σ8 √(m/0.3) compared to predictions from the standard cosmological model. Although some studies indicate that baryonic effects are too small to resolve this tension, others propose that more aggressive feedback mechanisms could reconcile differences between cosmic microwave background (CMB) measurements and low-redshift LSS observations. We investigate the role of baryonic effects in alleviating the S8 tension. We extend the SP(k) model, which was trained on hundreds of cosmological hydrodynamical simulations to map the suppression of the matter power spectrum to the baryon fraction in groups and clusters, to predict the required baryon fraction for a given P(k) suppression. We then compare predictions from recent cosmic shear (weak lensing) analyses with the latest baryon budget measurements from X-ray and weak gravitational lensing studies. Our findings show that studies marginalizing over baryonic effects while fixing cosmological parameters to a Planck-like cosmology predict strong P(k) suppression and baryon fractions that are much lower than existing low-redshift baryon budget estimates of galaxy groups and clusters. Conversely, most studies that marginalize over both cosmological parameters and baryonic effects imply baryon fractions that are consistent with observations but lower values of S8 than inferred from the CMB. Unless the observed baryon fractions are biased high by a factor of several, these results suggest that a mechanism beyond baryonic physics alone is required to modify or slow down the growth of structure in the universe in order to resolve the S8 tension.

Item Type:	Article
Uncontrolled Keywords:	large-scale structure of Universe; cosmology: theory; 5107 Particle and High Energy Physics; 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:	26 June 2026
Date of first compliant Open Access:	17 April 2026
Date Deposited:	17 Apr 2026 14:59
Last Modified:	17 Apr 2026 14:59
DOI or ID number:	10.1093/mnras/staf1055
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28396

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