The physics inside the scaling relations for X-ray galaxy clusters: gas clumpiness, gas mass fraction and slope of the pressure profile

Abstract

In galaxy clusters, the relations between observables in X-ray and millimeter wave bands and the total mass have normalizations, slopes and redshift evolutions that are simple to estimate in a self-similar scenario. We study these scaling relations and show that they can be efficiently expressed, in a more coherent picture, by fixing the normalizations and slopes to the self-similar predictions, and advocating, as responsible of the observed deviations, only three physical mass-dependent quantities: the gas clumpiness $C$, the gas mass fraction $f_g$ and the logarithmic slope of the thermal pressure profile ${\beta }_P$. We use samples of the observed gas masses, temperature, luminosities, and Compton parameters in local clusters to constrain normalization and mass dependence of these 3 physical quantities, and measure: $C^{0.5}{f}_g=0.110(\pm 0.002\pm 0.002){\left(E_{z}M/5\times 10^{14}{M}_{\odot }\right)}^{0.198(\pm 0.025\pm 0.04)}$ and ${\beta }_P=-d\ln P/d\ln r=3.14(\pm 0.04\pm 0.02){\left(E_{z}M/5\times 10^{14}{M}_{\odot }\right)}^{0.071(\pm 0.012\pm 0.004)}$, where both a statistical and systematic error (the latter mainly due to the cross-calibration uncertainties affecting the \cxo\ and \xmm\ results used in the present analysis) are quoted. The degeneracy between $C$ and $f_g$ is broken by using the estimates of the Compton parameters. Together with the self-similar predictions, these estimates on $C$, $f_g$ and ${\beta }_P$ define an inter-correlated internally-consistent set of scaling relations that reproduces the mass estimates with the lowest residuals.

11 pages, 4 figures. MNRAS in press

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• The X-ray luminosity-temperature relation of a complete sample of low-mass galaxy clusters
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• CoMaLit -- VI. Intrinsic scatter in stacked relations. The weak lensing AMICO galaxy clusters in KiDS-DR3
• Halo Concentrations and the New Baseline X-ray Luminosity-Temperature and Mass Relations of Galaxy Clusters