The Three Hundred Project: The evolution of galaxy cluster density profiles

Recent numerical studies of the dark matter density profiles of massive galaxy clusters ($M_{\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}>{10}^{15}$M${}_{\odot }$) show that their median radial mass density profile remains unchanged up to $z>1$, displaying a highly self-similar evolution. We verify this by using the data set of the THE THREE HUNDRED project, i.e. 324 cluster-sized haloes as found in full physics hydrodynamical simulations. We track the progenitors of the mass-complete sample of clusters at $z=0$, and find that their median shape is already in place by $z=2.5$. However, selecting a dynamically relaxed subsample ($\sim 16$ per cent of the clusters), we observe a shift of the scale radius $r_s$ towards larger values at earlier times. Classifying the whole sample by formation time, this evolution is understood as a result of a two-phase halo mass accretion process. Early-forming clusters – identified as relaxed today – have already entered their slow accretion phase, hence their mass growth occurs mostly at the outskirts. Late-forming clusters – which are still unrelaxed today – are in their fast accretion phase, thus the central region of the clusters is still growing. We conclude that the density profile of galaxy clusters shows a profound self-similarity out to redshifts $z\sim 2.5$. This result holds for both gas and total density profiles when including baryonic physics, as reported here for two rather distinct sub-grid models.