Satellite galaxy abundance dependency on cosmology in Magneticum simulations
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Context: Modelling satellite galaxy abundance N_s in Galaxy Clusters (GCs) is a key element in modelling the Halo Occupation Distribution (HOD), which itself is a powerful tool to connect observational studies with numerical simulations. Aims: To study the impact of cosmological parameters on satellite abundance both in cosmological simulations and in mock observations. Methods: We build an emulator (HODEmu, <https://github.com/aragagnin/HODEmu/>) of satellite abundance based on cosmological parameters Ω_m, Ω_b, σ_8, h_0 and redshift z. We train our emulator using hydrodynamic simulations that span 15 different cosmologies, each over 4 redshift slices between 0<z<0.5, and for each setup we fit normalisation A, log-slope β and Gaussian fractional-scatter σ of the N_s-M relation. The emulator is based on multi-variate output Gaussian Process Regression (GPR). Results: We find that A and β depend on cosmological parameters, even if weakly, especially on Ω_m, Ω_b. This dependency can explain some discrepancies found in literature between satellite HOD of different cosmological simulations (Magneticum, Illustris, BAHAMAS). We also show that satellite abundance cosmology dependency differs between full-physics (FP) simulations, dark-matter only (DMO), and non-radiative simulations. Conclusions: This work provides a preliminary calibration of the cosmological dependency of the satellite abundance of high mass halos, and we showed that modelling HOD with cosmological parameters is necessary to interpret satellite abundance, and we showed the importance of using FP simulations in modelling this dependency.
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