Baryon census in hydrodynamical simulations of galaxy clusters

We carry out an analysis of a set of cosmological smoothed particle hydrodynamics (SPH) hydrodynamical simulations of galaxy clusters and groups aimed at studying the total baryon budget in clusters, and how this budget is shared between the hot diffuse component and the stellar component. Using the TreePM+SPH GADGET-3 code, we carried out one set of non-radiative simulations, and two sets of simulations including radiative cooling, star formation and feedback from supernovae (SNe), one of which also accounting for the effect of feedback from active galactic nuclei (AGN). The analysis is carried out with the twofold aim of studying the implication of stellar and hot gas content on the relative role played by SNe and AGN feedback, and to calibrate the cluster baryon fraction and its evolution as a cosmological tool. With respect to previous similar analysis, the simulations used in this study provide us with a sufficient statistics of massive objects and including an efficient AGN feedback. We find that both radiative simulation sets predict a trend of stellar mass fraction with cluster mass that tends to be weaker than the observed one. However this tension depends on the particular set of observational data considered. Including the effect of AGN feedback alleviates this tension on the stellar mass and predicts values of the hot gas mass fraction and total baryon fraction to be in closer agreement with observational results. We further compute the ratio between the cluster baryon content and the cosmic baryon fraction, Y-b, as a function of clustercentric radius and redshift. At R-500 we find for massive clusters with M-500 > 2 x 10(14) h(-1) M-circle dot that Y-b is nearly independent of the physical processes included and characterized by a negligible redshift evolution: Y-b,Y-500 = 0.85 +/- 0.03 with the error accounting for the intrinsic rms scatter within the set of simulated clusters. At smaller radii, R-2500, the typical value of Y-b slightly decreases, by an amount that depends on the physics included in the simulations, while its scatter increases by about a factor of 2. These results have interesting implications for the cosmological applications of the baryon fraction in clusters.