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Using cosmological simulations of galaxy cluster regions from The Three Hundred project, we study the nature of gas in filaments feeding massive clusters. By stacking the diffuse material of filaments throughout the cluster sample, we measure average gas properties such as density, temperature, pressure, entropy and Mach number and construct one-dimensional profiles for a sample of larger, radially oriented filaments to determine their characteristic features as cosmological objects. Despite the similarity in velocity space between the gas and dark matter accretion patterns on to filaments and their central clusters, we confirm some differences, especially concerning the more ordered radial velocity dispersion of dark matter around the cluster and the larger accretion velocity of gas relative to dark matter in filaments. We also study the distribution of shocked gas around filaments and galaxy clusters, showing that the surrounding shocks allow an efficient internal transport of material, suggesting a laminar infall. The stacked temperature profile of filaments is typically colder towards the spine, in line with the cosmological rarefaction of matter. Therefore, filaments are able to isolate their inner regions, maintaining lower gas temperatures and entropy. Finally, we study the evolution of the gas density–temperature phase diagram of our stacked filament, showing that filamentary gas does not behave fully adiabatically through time but it is subject to shocks during its evolution, establishing a characteristic z  = 0, entropy-enhanced distribution at intermediate distances from the spine of about |$1{-}2\, h^{-1}\,$|  Mpc for a typical galaxy cluster in our sample. [ABSTRACT FROM AUTHOR]

Using the data set of the three hundred project, i.e. a suite of 324 hydrodynamical resimulations of cluster-sized haloes, we study galaxy cluster mergers and their effect on colour and luminosity changes of their brightest cluster galaxies (BCG). We track the main progenitor of each halo at z = 0 and search for merger situations based on its mass accretion history, defining mergers as very rapid increases in the halo mass. Based upon the evolution of the dynamical state of the cluster we define a pre- and post-merger phase. We create a list of all these events and statistically study their mass ratio and time-scales, with the former verifying that all instances are in fact major mergers. By comparing to a control sample of clusters without mergers, we study the effect mergers have on the stellar component of the BCG. Analysing the mass, age, and metallicity of the BCG stellar particles, we find that the stellar content of BCGs grows significantly during mergers and, even though the main growth mechanism is the accretion of older stars, there is even a burst in star formation induced by the merger. In our simulations, BCGs in mergers form in median around 70 per cent more stars than those normally growing, although this depends on the radius considered for defining the BCG. Regarding observable properties, we see an increase in SDSS- u luminosity of 20 per cent during mergers, accompanied by a slightly slower increase of the galaxy g − r colour as compared to the control sample. [ABSTRACT FROM AUTHOR]

Radio relics in galaxy clusters are believed to trace merger shock fronts. If cosmological structure formation determines the luminosity, size and shape distributions of radio relics, then merger shocks need to be lighted up in a homogeneous way. We investigate if a mock relic sample, obtained from zoomed galaxy cluster simulations, is able to match the properties of relics measured in the NRAO VLA Sky Survey (NVSS). We compile a list of all radio relics known to date and homogeneously measure their parameters in all NVSS images and apply the same procedure to relics in our simulations. Number counts in the mock relic sample increase more steeply towards lower relic flux densities, suggesting an incompleteness of NVSS in this regime. Overall, we find that NVSS and mock samples show similar properties. However, large simulated relics tend to be somewhat smaller and closer to the cluster centre than observed ones. Besides this, the mock sample reproduces very well-known correlations for radio relics, in particular those relating the radio luminosity with the largest linear size and the X-ray luminosity. We show that these correlations are largely governed by the sensitivity of the NVSS observations. Mock relics show a similar orientation with respect to the direction to the cluster centre as the NVSS sample. Moreover, we find that their maximum radio luminosity roughly correlates with cluster mass, although displaying a large scatter. The overall good agreement between NVSS and the mock sample suggests that properties of radio relics are indeed governed by merger shock fronts, emitting in a homogeneous fashion. Our study demonstrates that the combination of mock observations and data from upcoming radio surveys will allow us to shed light on both the origin of radio relics and the nature of the intracluster medium. [ABSTRACT FROM AUTHOR]

ABSTRACT We explore the possibility of detecting radio emission in the cosmic web by analysing shock waves in the MareNostrum cosmological simulation. This requires a careful calibration of shock finding algorithms in smoothed particle hydrodynamics simulations, which we present here. Moreover, we identify the elements of the cosmic web, namely voids, walls, filaments and clusters with the use of the SpineWeb technique, a procedure that classifies the structure in terms of its topology. Thus, we are able to study the Mach number distribution as a function of its environment. We find that the median Mach number for clusters is , for filaments is , for walls is and for voids is . We then estimate the radio emission in the cosmic web using the formalism derived in Hoeft & Brüggen. We also find that in order to match our simulations with observational data [e.g. NRAO VLA Sky Survey (NVSS) radio relic luminosity function], a fraction of energy dissipated at the shock of ξe= 0.0005 is needed, in contrast with the ξe= 0.005 proposed by Hoeft et al. We find that 41 per cent of clusters with M≥ 1014 M⊙ host diffuse radio emission in the form of radio relics. Moreover, we predict that the radio flux from filaments should be Jy at a frequency of 150 MHz. [ABSTRACT FROM AUTHOR]