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

TL;DR

This study uses cosmological simulations to analyze baryon distributions in massive halos, revealing how baryon fractions vary with radius and mass, and providing simple predictive models for these properties.

Contribution

It offers the first detailed analysis of baryon, gas, and star distributions out to 10 times the virial radius in massive halos, with simple functional forms describing their radial and mass dependencies.

Findings

Baryon fraction increases with radius, approaching cosmic values at large distances.

Star mass fraction is higher in less massive halos and stabilizes at ~0.09.

Gas metallicity remains constant across different halo masses.

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 $10 R_{500,\mathrm c}$. 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 ($r>6 R_{500,\mathrm c}$), where the baryon depletion factor $Y_{\rm bar} = f_{\rm bar} / (\Omega_{\rm b}/\Omega_{\rm m})$ 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 $Y_{\rm star} \approx 0.09$, where also the gas metallicity is constant, regardless of the host halo mass, as a result of the early ($z>2$) enrichment process.