Shock and Splash: Gas and Dark Matter Halo Boundaries around LambdaCDM Galaxy Clusters

TL;DR

This study uses hydrodynamical simulations to analyze the physical boundaries of galaxy clusters, revealing that the accretion shock boundary is significantly larger than the dark matter splashback radius, challenging previous models.

Contribution

It provides new insights into the offset between accretion shock and splashback radii in galaxy clusters, based on detailed simulation analysis.

Findings

Accretion shock radius exceeds splashback radius by 20-100%.

Shock radius is about twice the splashback radius defined by entropy profiles.

Shock boundary is approximately 1.2 times larger than the dark matter phase-space edge.

Abstract

Recent advances in simulations and observations of galaxy clusters suggest that there exists a physical outer boundary of massive cluster-size dark matter haloes. In this work, we investigate the locations of the outer boundaries of dark matter and gas around cluster-size dark matter haloes, by analyzing a sample of 65 massive dark matter halos extracted from the Omega500 zoom-in hydrodynamical cosmological simulations. We show that the location of accretion shock is offset from that of the dark matter 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%. The accretion shock radius defined using the steepest drop in the entropy pressure profiles is approximately 2 times larger than the splashback radius defined by the steepest slope in the dark matter density profile, and it is ~1.2 times larger than the edge of the dark matter phase-space structure. We discuss implications of our results for multi-wavelength studies of galaxy clusters.