Shock and splash: gas and dark matter halo boundaries around ΛCDM galaxy clusters

Recent advances in simulations and observations of galaxy clusters suggest that there exists a physical outer boundary of massive cluster-size dark matter (DM) haloes. In this work, we investigate the locations of the outer boundaries of DM and gas around cluster-size DM haloes, by analysing a sample of 65 massive DM haloes extracted from the Omega500 zoom-in hydrodynamical cosmological simulations. We show that the location of accretion shock is offset from that of the DM splashback radius, contrary to the prediction of the self-similar models. The accretion shock radius is larger than all definitions of the splashback radius in the literature by 20 - 100 per cent. The accretion shock radius defined using the steepest drop in the entropy and pressure profiles is approximately 1.89 times larger than the splashback radius defined by the steepest slope in the DM density profile, and it is approximate to 1.2 times larger than the edge of the DM phase space structure. We discuss implications of our results for multiwavelength studies of galaxy clusters.

Automated summary

Recent studies have found discrepancies between the location of the accretion shock and the splashback radius of dark matter, with the former being larger by 20-100%. This has implications for multiwavelength studies of galaxy clusters.