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

Abstract

We study the distributions of the baryons in massive halos ($M_{vir}>10^{13}{h}^{-1}{M}_{\odot }$) in the $Magneticum$ suite of Smoothed Particle Hydrodynamical cosmological simulations, out to the unprecedented radial extent of $10R_{500,\mathrm{c}}$. We confirm that, under the action of non-gravitational physical phenomena, the baryon mass fraction is lower in the inner regions ($<R_{500,\mathrm{c}}$) of increasingly less massive halos, and rises moving outwards, with values that spans from 51% (87%) in the regions around $R_{500,\mathrm{c}}$ to 95% (100%) at $10R_{500,\mathrm{c}}$ of the cosmological value in the systems with the lowest (highest; $M_{vir}\sim 5\times 10^{14}{h}^{-1}{M}_{\odot }$) masses. The galaxy groups almost match the gas (and baryon) fraction measured in the most massive halos only at very large radii ($r>6R_{500,\mathrm{c}}$), where the baryon depletion factor $Y_{\mathrm{bar}}=f_{\mathrm{bar}}/(\hat{I}{\text{c◯}}_{\mathrm{b}}/\hat{I}{\text{c◯}}_{\mathrm{m}})$ approaches the value of unity, expected for "closed-box" systems. We find that both the radial and mass dependency 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 $Y_{\mathrm{star}}\approx 0.09$, where also the gas metallicity is constant, regardless of the host halo mass, as a result of the early ($z>2$) enrichment process.

Submitted to A&A; 9 pages, 6 figures