Mapping 'out-of-the-box' the properties of the baryons in massive halos

We study the distributions of the baryons in massive halos ( M vir > 10 13 h − 1 M (cid:12) ) in the Magneticum suite of smoothed particle hydrodynamical cosmological simulations, out to the unprecedented radial extent of 10 R 500 , c . We confirm that, under the action of non-gravitational physical phenomena, the baryon mass fraction is lower in the inner regions ( < R 500 , c ) of increasingly less massive halos, and rises moving outwards, with values that span from 51% (87%) of the cosmological value in the regions around R 500 , c to 95% (100%) at 10 R 500 , c in the systems with the lowest (highest; M vir ∼ 5 × 10 14 h − 1 M (cid:12) ) masses. The galaxy groups almost match the gas (and baryon) fraction measured in the most massive halos only at very large radii ( r > 6 R 500 , c ), where the baryon depletion factor Y bar = f bar / ( Ω b / Ω m ) approaches the value of unity, expected for ‘closed-box’ systems. We find that both the radial and mass dependence of the baryon, gas, and hot depletion factors are predictable and follow a simple functional form. The star mass fraction is higher in less massive systems, decreases systematically with increasing radii, and reaches a constant value of Y star ≈ 0 . 09, where the gas metallicity is also constant, regardless of the host halo mass, as a result of the early ( z > 2) enrichment process.