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) N_sat, the number of stellar mass-thresholded satellite galaxies within radius R_200c 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 N_sat - M_⋆,BCG correlation. Marginalizing over M_halo, we find the N_sat kernel, p(ln N_sat | M_halo,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 N_sat kernel as well as local linear regression parameters tabulated for M_halo > 10^13.5 M⊙ in all simulations.