Stellar property statistics of massive haloes from cosmological hydrodynamics simulations: common kernel shapes

We study stellar property statistics, including satellite galaxy occupation, of haloes in three cosmological hydrodynamics simulations: BAHAMAS + MACSIS, IllustrisTNG, and Magneticum Pathfinder. Applying localized linear regression, we extract halo mass-conditioned normalizations, slopes, and intrinsic covariance for (i) Nsat, the number of stellar mass-thresholded satellite galaxies within radius R200c of the halo; (ii) M, tot, the total stellar mass within that radius, and (iii) M, BCG, the gravitationally bound stellar mass of the central galaxy within a 100 \, kpc radius. The parameters show differences across the simulations, in part from numerical resolution, but there is qualitative agreement for the Nₛₐₜ\!-\! M, BCG correlation. Marginalizing over Mhalo, we find the Nsat kernel, p(ln Nₛₐₜ\, |\, Mₕₐₗₒ, z) to be consistently skewed left in all three simulations, with skewness parameter γ = −0.91 ± 0.02, while the M, tot kernel shape is closer to lognormal. The highest resolution simulations find γ ≃ −0.8 for the z = 0 shape of the M, BCG kernel. We provide a Gaussian mixture fit to the low-redshift Nsat kernel as well as local linear regression parameters tabulated for Mₕₐₗₒ> 1013.5 \, M_ in all simulations.