SIMBAD references

We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ≤ z ≤ 1 are selected from the COSMOS 2 deg² survey, based only on their X-ray luminosity and extent. This sample is complemented by 27 nearby clusters with a robust, analogous determination of the total and stellar mass inside R₅₀₀. The total sample of 118 groups and clusters with z ≤ 1 spans a range in M₅₀₀ of ∼10¹³-10¹⁵ M_☉. We find that the stellar mass fraction associated with galaxies at R₅₀₀decreases with increasing total mass as M ^{–0.37±0.04}₅₀₀, independent of redshift. Estimating the total gas mass fraction from a recently derived, high-quality scaling relation, the total baryon mass fraction (f ^stars+gas₅₀₀= f ^stars₅₀₀+ f ^gas₅₀₀) is found to increase by ∼25%, when M₅₀₀ increases from = 5x10¹³ M_☉ to = 7x10¹⁴ M_☉. After consideration of a plausible contribution due to intracluster light (11%-22% of the total stellar mass) and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.3σ for groups of = 5x10¹³ M_☉. The discrepancy decreases toward higher total masses, such that it is 1σ at = 7x10¹⁴ M_☉. We discuss this result in terms of nongravitational processes such as feedback and filamentary heating.