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    Constancy of the cluster gas mass fraction in the Rh=ct Universe

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    Author
    Melia, Fulvio cc
    Affiliation
    The University of Arizona
    Issue Date
    2016-02-17
    
    Metadata
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    Publisher
    The Royal Society
    Citation
    Constancy of the cluster gas mass fraction in the Rh=ct Universe 2016, 472 (2186):20150765 Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science
    Journal
    Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science
    Rights
    © 2016 The Author(s) Published by the Royal Society. All rights reserved.
    Collection Information
    This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.
    Abstract
    The ratio of baryonic to dark matter densities is assumed to have remained constant throughout the formation of structure. With this, simulations show that the fraction $f_{\rm gas}(z)$ of baryonic mass to total mass in galaxy clusters should be nearly constant with redshift $z$. However, the measurement of these quantities depends on the angular distance to the source, which evolves with $z$ according to the assumed background cosmology. An accurate determination of $f_{\rm gas}(z)$ for a large sample of hot ($kT_e> 5$ keV), dynamically relaxed clusters could therefore be used as a probe of the cosmological expansion up to $z< 2$. The fraction $f_{\rm gas}(z)$ would remain constant only when the ``correct" cosmology is used to fit the data. In this paper, we compare the predicted gas mass fractions for both $\Lambda$CDM and the $R_{\rm h}=ct$ Universe and test them against the 3 largest cluster samples \cite{1,2,3}. We show that $R_{\rm h}=ct$ is consistent with a constant $f_{\rm gas}$ in the redshift range $z\lesssim 2$, as was previously shown for the reference $\Lambda$CDM model (with parameter values $H_0=70$ km s$^{-1}$ Mpc$^{-1}$, $\Omega_m=0.3$ and $w_\Lambda=-1$). Unlike $\Lambda$CDM, however, the $R_{\rm h}=ct$ Universe has no free parameters to optimize in fitting the data. Model selection tools, such as the Akaike Information Criterion (AIC) and the Bayes Information Criterion (BIC), therefore tend to favor $R_{\rm h}=ct$ over $\Lambda$CDM. For example, the BIC favours $R_{\rm h}=ct$ with a likelihood of $\sim 95\%$ versus $\sim 5\%$ for $\Lambda$CDM.
    Note
    Published 17 February 2016. 12 month embargo.
    ISSN
    1364-5021
    1471-2946
    DOI
    10.1098/rspa.2015.0765
    Version
    Final accepted manuscript
    Additional Links
    http://rspa.royalsocietypublishing.org/lookup/doi/10.1098/rspa.2015.0765
    ae974a485f413a2113503eed53cd6c53
    10.1098/rspa.2015.0765
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