Letter to the Editor

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

¹ Dipartimento di Fisica e Astronomia, Universitá di Bologna, Via Gobetti 92/3, 40121 Bologna, Italy
e-mail: matteo.angelinelli2@unibo.it
² INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via Pietro Gobetti 93/3, 40121 Bologna, Italy
³ INFN, Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
⁴ Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr.1, 81679 München, Germany
⁵ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany
⁶ Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁷ Istituto di Radio Astronomia, INAF, Via Gobetti 101, 40121 Bologna, Italy
⁸ INAF, Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34143 Trieste, Italy
⁹ IFPU, Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy

Received: 20 May 2022
Accepted: 23 June 2022

Abstract

We study the distributions of the baryons in massive halos (M_vir > 10¹³ h⁻¹ M_⊙) in the Magneticum suite of smoothed particle hydrodynamical cosmological simulations, out to the unprecedented radial extent of 10R_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 10R_500, c in the systems with the lowest (highest; M_vir ∼ 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 > 6R_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.