We present an analysis of the relation between the masses of cluster-and group-sized halos, extracted from ΛCDM cosmological N-body and hydrodynamic simulations, and their velocity dispersions, at different redshifts from z = 2 to z = 0. The main aim of this analysis is to understand how the implementation of baryonic physics in simulations affects such relation, i.e. to what extent the use of the velocity dispersion as a proxy for cluster mass determination is hampered by the imperfect knowledge of the baryonic physics. In our analysis we use several sets of simulations with different physics implemented: one DM-only simulation, one simulation with non-radiative gas, and two radiative simulations, one of which with feedback from Active Galactic Nuclei. Velocity dispersions are determined using three different tracers, dark matter (DM hereafter) particles, subhalos, and galaxies.We confirm that DM particles trace a relation that is fully consistent with the theoretical expectations based on the virial theorem, σ v ∝ M α with α = 1/3, and with previous results presented in the literature. On the other hand, subhalos and galaxies trace steeper relations, with velocity dispersion scaling with mass with α > 1/3, and with larger values of the normalization. Such relations imply that galaxies and subhalos have a ∼ 10 per cent velocity bias relative to the DM particles, which can be either positive or negative, depending on halo mass, redshift and physics implemented in the simulation.We explain these differences as due to dynamical processes, namely dynamical friction and tidal disruption, acting on substructures and galaxies, but not on DM particles. These processes appear to be more or less effective, depending on the halo masses and the importance of baryon cooling, and may create a non-trivial dependence of the velocity bias and the σ 1D -M 200 relation on the tracer, the halo mass and its redshift.These results are relevant in view of the application of velocity dispersion as a proxy for cluster masses in ongoing and future large redshift surveys.

We present a study of the effect of active galactic nuclei (AGN) feedback on metal enrichment and thermal properties of the intracluster medium (ICM) in hydrodynamical simulations of galaxy clusters. The simulations are performed using a version of the TreePM–sphgadget‐2 code, which also follows chemodynamical evolution by accounting for metal enrichment contributed by different stellar populations. We carry out cosmological simulations for a set of galaxy clusters, covering the mass range M200≃ (0.1–2.2) × 1015 h−1 M⊙. Besides runs not including any efficient form of energy feedback, we carry out simulations including three different feedback schemes: (i) kinetic feedback in the form of galactic winds triggered by supernova explosions; (ii) AGN feedback from gas accretion on to supermassive black holes (BHs) and (iii) AGN feedback in which a ‘radio mode’ is included with an efficient thermal coupling of the extracted energy, whenever BHs enter in a quiescent accretion phase. Besides investigating the resulting thermal properties of the ICM, we analyse in detail the effect that these feedback models have on the ICM metal enrichment. We find that AGN feedback has the desired effect of quenching star formation in the brightest cluster galaxies at z < 4 and provides correct temperature profiles in the central regions of galaxy groups. However, its effect is not yet sufficient to create ‘cool cores’ in massive clusters while generating an excess of entropy in central regions of galaxy groups. As for the pattern of metal distribution, AGN feedback creates a widespread enrichment in the outskirts of clusters, thanks to its efficiency in displacing enriched gas from galactic haloes to the intergalactic medium. This turns into profiles of iron abundance, ZFe, which are in better agreement with observational results, and into a more pristine enrichment of the ICM around and beyond the cluster virial regions. Following the pattern of the relative abundances of silicon and iron, we conclude that a significant fraction of the ICM enrichment is contributed in simulations by a diffuse population of intracluster stars. Our simulations also predict that profiles of the ZSi/ZFe abundance ratio do not increase at increasing radii, at least out to 0.5Rvir. Our results clearly show that different sources of energy feedback leave distinct imprints in the enrichment pattern of the ICM. They further demonstrate that such imprints are more evident when looking at external regions, approaching the cluster virial boundaries.

We carry out an analysis of a set of cosmological SPH hydrodynamical simulations of galaxy clusters and groups aimed at studying the total baryon budget in clusters, and how this budget is shared between the hot diffuse component and the stellar component. Using the TreePM+SPH GADGET-3 code, we carried out one set of non-radiative simulations, and two sets of simulations including radiative cooling, star formation and feedback from supernovae (SN), one of which also accounting for the effect of feedback from active galactic nuclei (AGN). The analysis is carried out with the twofold aim of studying the implication of stellar and hot gas content on the relative role played by SN and AGN feedback, and to calibrate the cluster baryon fraction and its evolution as a cosmological tool. With respect to previous similar analysis, the simulations used in this study provide us with a sufficient statistics of massive objects and including an efficient AGN feedback. We find that both radiative simulation sets predict a trend of stellar mass fraction with cluster mass that tends to be weaker than the observed one. However this tension depends on the particular set of observational data considered. Including the effect of AGN feedback alleviates this tension on the stellar mass and predicts values of the hot gas mass fraction and total baryon fraction to be in closer agreement with observational results. We further compute the ratio between the cluster baryon content and the cosmic baryon fraction, Y b , as a function of cluster-centric radius and redshift. At R 500 we find for massive clusters with M 500 > 2 × 10 14 h −1 M ⊙ that Y b is nearly independent of the physical processes included and characterized by a negligible redshift evolution: Y b,500 = 0.85 ± 0.03 with the error accounting for the intrinsic r.m.s. scatter within the set of simulated clusters. At smaller radii, R 2500 , the typical value of Y b slightly decreases, by an amount that depends on the physics included in the simulations, while its scatter increases by about a factor of two. These results have interesting implications for the cosmological applications of the baryon fraction in clusters.