Simulating the effect of active galactic nuclei feedback on the metal enrichment of galaxy clusters

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-SPH GADGET-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 M-200 similar or equal to (0.1-2.2) x 10(15) h(-1)M(circle dot). 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, Z(Fe), 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 Z(Si)/Z(Fe) abundance ratio do not increase at increasing radii, at least out to 0.5 R-vir. 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.