Mapping ‘out-of-the-box’ the properties of the baryons in massive halos

Abstract

We study the distributions of the baryons in massive halos (Mvir > 1013 h−1 M⊙) 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 × 1014 h−1 M⊙) 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-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 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.