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

Abstract

We study the distributions of the baryons in massive halos (Mvir > 1013h 1M-) in the Magneticum suite of smoothed particle hydrodynamical cosmological simulations, out to the unprecedented radial extent of 10R500,c. We confirm that, under the action of non-gravitational physical phenomena, the baryon mass fraction is lower in the inner regions (< R500,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 R500,c to 95% (100%) at 10R500,c in the systems with the lowest (highest; Mvir 5 - 1014h 1M-) masses. The galaxy groups almost match the gas (and baryon) fraction measured in the most massive halos only at very large radii (r > 6R500,c), where the baryon depletion factor Ybar = fbar/(Ωb/Ωm) approaches the value of unity, expected for 'closed-boxa'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 Ystar 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.