STELLAR AND TOTAL BARYON MASS FRACTIONS IN GROUPS AND CLUSTERS SINCE REDSHIFT 1

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 deg(2) 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 R(500). The total sample of 118 groups and clusters with z <= 1 spans a range in M(500) of similar to 10(13)-10(15) M(circle dot). We find that the stellar mass fraction associated with galaxies at R(500) decreases with increasing total mass as M(500)(-0.37+/-0.04), independent of redshift. Estimating the total gas mass fraction from a recently derived, high-quality scaling relation, the total baryon mass fraction (f(500)(stars+gas) = f(500)(stars) + f(500)(gas)) is found to increase by similar to 25%, when M(500) increases from < M > = 5 x 10(13) M(circle dot) to < M > = 7 x 10(14)M(circle dot). 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 3.3 sigma for groups of < M > = 5 x 10(13) M(circle dot). The discrepancy decreases toward higher total masses, such that it is 1 sigma at < M > = 7 x 10(14) M(circle dot). We discuss this result in terms of nongravitational processes such as feedback and filamentary heating.