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Cluster gas fraction as a test of gravity

Li, B.; He, J.; Gao, L.

Cluster gas fraction as a test of gravity Thumbnail


J. He

L. Gao


We propose a new cosmological test of gravity, by using the observed mass fraction of X-ray-emitting gas in massive galaxy clusters. The cluster gas fraction, believed to be a fair sample of the average baryon fraction in the Universe, is a well-understood observable, which has previously mainly been used to constrain background cosmology. In some modified gravity models, such as f(R) gravity, gas temperature in a massive cluster is determined by the effective mass (the mass that would have produced the same gravitational effect assuming standard gravity as the cluster actually does in f(R) gravity) of that cluster, which can be larger than its true mass. On the other hand, X-ray luminosity is determined by the true gas density, which in both modified gravity and Λ-cold-dark-matter models depends mainly on Ωb/Ωm and hence the true total cluster mass. As a result, the standard practice of combining gas temperatures and X-ray surface brightnesses of clusters to infer their gas fractions can, in modified gravity models, lead to a larger – in f(R) gravity this can be 1/3 larger – value of Ωb/Ωm than that inferred from other observations such as the cosmic microwave background. Our quick calculation shows that the Hu–Sawicki n = 1 f(R) model with |f¯R0|=5×10−5|f¯R0|=5×10−5 is in tension with the gas fraction data of the 42 clusters analysed by Allen et al. We also discuss the implications for other modified gravity models.


Li, B., He, J., & Gao, L. (2016). Cluster gas fraction as a test of gravity. Monthly Notices of the Royal Astronomical Society, 456(1), 146-155.

Journal Article Type Article
Acceptance Date Nov 7, 2015
Online Publication Date Dec 11, 2015
Publication Date Feb 11, 2016
Deposit Date Feb 18, 2016
Publicly Available Date Feb 18, 2016
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 456
Issue 1
Pages 146-155
Keywords Methods: analytical, Methods: statistical, Galaxies: haloes, Cosmological parameters, Dark matter, Large-scale structure of Universe.


Published Journal Article (439 Kb)

Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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