We introduce the The Three Hundred project, an endeavour to model 324 large galaxy clusters with full-physics hydrodynamical re-simulations. Here we present the dataset and study the differences to observations for fundamental galaxy cluster properties and scaling relations. We find that the modelled galaxy clusters are generally in reasonable agreement with observations with respect to baryonic fractions and gas scaling relations at redshift z = 0. However, there are still some (model-dependent) differences, such as central galaxies being too massive, and galaxy colours (g −r) being bluer (about 0.2 dex lower at the peak position) than in observations. The agreement in gas scaling relations down to 10 13 h −1 M between the simulations indicates that particulars of the sub-grid modelling of the baryonic physics only has a weak influence on these relations. We also include -where appropriate -a comparison to three semianalytical galaxy formation models as applied to the same underlying dark matter only simulation. All simulations and derived data products are publicly available.observed properties of the Intra-Cluster Medium (ICM), the size of the central brightest cluster galaxy and the number and properties of the satellite galaxies orbiting within a common dark matter envelope. Clusters of galaxies can therefore be considered to be large cosmological laboratories that are useful for pinning down both cosmological parameters and empirical models of astrophysical processes acting across a range of coupled scales.Concerted effort, from both observational and theoretical perspectives, has been devoted to improve our understanding of the formation and evolution of galaxy clusters. On the observational side, multi-wavelength telescopes are

We present an analysis of the effects of baryon physics on the halo mass function. The analysis is based on simulations of a cosmological volume having a comoving size of 410 h-1 Mpc, which have been carried out with the TREE-PM/smoothed particle hydrodynamics code GADGET-3, for a Wilkinson Microwave Anisotropy Probe-7 Λ cold dark matter cosmological model. Besides a dark matter (DM)-only simulation, we also carry out two hydrodynamical simulations: the first one includes non-radiative physics, with gas heated only by gravitational processes; the second one includes radiative cooling, star formation and kinetic feedback in the form of galactic ejecta triggered by supernova explosions. All simulations follow the evolution of two populations of 10243 particles each, with mass ratio such that to reproduce the assumed baryon density parameter, with the population of lighter particles assumed to be collisional in the hydrodynamical runs. We identified haloes using a spherical overdensity algorithm and their masses are computed at three different overdensities (with respect to the critical one), Δc= 200, 500 and 1500. We find the fractional difference between halo masses in the hydrodynamical and in the DM simulations to be almost constant, at least for haloes more massive than ?. In this range, mass increase in the hydrodynamical simulations is of about 4-5 per cent at Δc= 500 and ˜1-2 per cent at Δc= 200. Quite interestingly, these differences are nearly the same for both radiative and non-radiative simulations. Mass variations depend on halo mass and physics included for higher overdensity, Δc= 1500, and smaller masses. Such variations of halo masses induce corresponding variations of the halo mass function (HMF). At z= 0, the HMFs for gravitational heating and cooling and star formation simulations are close to the DM one, with differences of ≲3 per cent at Δc= 200, and ≃7 per cent at Δc= 500, with ˜10-20 per cent differences reached at Δc= 1500. At this higher overdensity, the increase of the HMF for the radiative case is larger by about a factor of 2 with respect to the non-radiative case. Assuming a constant mass shift to rescale the HMF from the hydrodynamic to the DM simulations, brings the HMF difference with respect to the DM case to be consistent with zero, with a scatter of ≲3 per cent at Δc= 500 and ≲2 per cent at Δc= 200. Our results have interesting implications for assessing uncertainties in the mass function calibration associated with the uncertain baryon physics, in view of cosmological applications of future large surveys of galaxy clusters

In this paper, we carry out a detailed analysis of the performance of two different methods to identify the diffuse stellar light in cosmological hydrodynamical simulations of galaxy clusters. One method is based on a dynamical analysis of the stellar component, which separates the brightest central galaxy (BCG) from the stellar component not gravitationally bound to any galaxy, what we call 'diffuse stellar component' (DSC). The second method is closer to techniques commonly employed in observational studies. We generate mock images from simulations, and assume a standard surface brightness limit (SBL) to disentangle the BCG from the intra-cluster light (ICL). Both the dynamical method and the method based on the SBL criterion are applied to the same set of hydrodynamical simulations for a large sample of about 80 galaxy clusters. We analyse two sets of radiative simulations: a first set includes the effect of cooling, star formation, chemical enrichment and galactic outflows triggered by supernova feedback (CSF set); a second one also includes the effect of thermal feedback from active galactic nuclei triggered by gas accretion on to supermassive black holes (AGN set).We find significant differences between the ICL and DSC fractions computed with the two corresponding methods, which amounts to about a factor of 2 for the AGN simulations, and a factor of 4 for the CSF set. We also find that the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of 1.5-2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to decrease from ∼ 80 per cent in galaxy groups to ∼ 60 per cent in rich clusters, thus in excess of that found from observational analysis.We identify the average SBLs that yield the ICL fraction from the SBL method close to the DSC fraction from the dynamical method. These SBLs turn out to be brighter in the CSF than in the AGN simulations. This is consistent with the finding that AGN feedback makes BCGs to be less massive and with shallower density profiles than in the CSF simulations. The BCG stellar components, as identified by both methods, are slightly older and more metal-rich than the stars in the diffuse component. Relaxed clusters have somewhat higher stellar mass fractions in the diffuse component. The metallicity and age of both the BCG and diffuse components in relaxed clusters are also richer in metals and older.

In the outer regions of a galaxy cluster, galaxies may be either falling into the cluster for the first time, or have already passed through the cluster centre at some point in their past. To investigate these two distinct populations, we utilise TheThreeHundred project, a suite of 324 hydrodynamical resimulations of galaxy clusters. In particular, we study the 'backsplash population' of galaxies; those that have passed within R 200 of the cluster centre at some time in their history, but are now outside of this radius. We find that, on average, over half of all galaxies between R 200 and 2R 200 from their host at z = 0 are backsplash galaxies, but that this fraction is dependent on the dynamical state of a cluster, as dynamically relaxed clusters have a greater backsplash fraction. We also find that this population is mostly developed at recent times (z 0.4), and is dependent on the recent history of a cluster. Finally, we show that the dynamical state of a given cluster, and thus the fraction of backsplash galaxies in its outskirts, can be predicted based on observational properties of the cluster.