Open AccessRevisiting the baryon fractions of galaxy clusters: a comparison with WMAP 3‐yr results
Author(s) -
McCarthy I. G.,
Bower R. G.,
Balogh M. L.
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2007.11733.x
Subject(s) - cmb cold spot , physics , cosmic microwave background , astrophysics , baryon , mass fraction , galaxy cluster , galaxy , cosmic background radiation , redshift , anisotropy , thermodynamics , quantum mechanics
The universal baryonic mass fraction (Ω b /Ω m ) can be sensitively constrained using X‐ray observations of galaxy clusters. In this paper, we compare the baryonic mass fraction inferred from measurements of the cosmic microwave background with the gas mass fractions ( f gas ) of a large sample of clusters taken from the recent literature. In systems cooler than 4 keV, f gas declines as the system temperature decreases. However, in higher temperature systems, f gas ( r 500 ) converges to ≈(0.12 ± 0.02)( h /0.72) −1.5 , where the uncertainty reflects the systematic variations between clusters at r 500 . This is significantly lower than the maximum‐likelihood value of the baryon fraction from the recently released Wilkinson Microwave Anisotropy Probe ( WMAP ) 3‐yr results. We investigate possible reasons for this discrepancy, including the effects of radiative cooling and non‐gravitational heating, and conclude that the most likely solution is that Ω m is higher than the best‐fitting WMAP value (we find Ω m = 0.36 +0.11 −0.08 ), but consistent at the 2σ level. Degeneracies within the WMAP data require that σ 8 must also be greater than the maximum likelihood value for consistency between the data sets.