Testing Strict Hydrostatic Equilibrium in Simulated Clusters of Galaxies: Implications for A1689

Abstract

Accurate mass determination of clusters of galaxies is crucial if they are to be used as cosmological probes. However, there are some discrepancies between cluster masses determined based on gravitational lensing and X-ray observations assuming strict hydrostatic equilibrium (i.e., the equilibrium gas pressure is provided entirely by thermal pressure). Cosmological simulations suggest that turbulent gas motions remaining from hierarchical structure formation may provide a significant contribution to the equilibrium pressure in clusters. We analyze a sample of massive clusters of galaxies drawn from high-resolution cosmological simulations and find a significant contribution (20%-45%) from non-thermal pressure near the center of relaxed clusters, and, in accord with previous studies, a minimum contribution at about 0.1 R vir , growing to about 30%-45% at the virial radius, R vir. Our results strongly suggest that relaxed clusters should have significant non-thermal support in their core region. As an example, we test the validity of strict hydrostatic equilibrium in the well-studied massive galaxy cluster A1689 using the latest high-resolution gravitational lensing and X-ray observations. We find a contribution of about 40% from non-thermal pressure within the core region of A1689, suggesting an alternate explanation for the mass discrepancy: the strict hydrostatic equilibrium is not valid in this region.

Nonthermal support for the outer intracluster medium

“…This demands closer probing, which we have tackled with the fast, analytic tool provided by the SM. The present data from joint X-ray and weak lensing observations (see Kawaharada et al 2010;Molnar et al 2010;Zhang et al 2010) concur with simulations (see Lau et al 2009) to show no evidence of a dissipation scale that is much shorter than ∼10 2 kpc, conceivably set by tangling of the magnetic field (see discussions by Narayan & Medvedev 2001;Brunetti & Lazarian 2007).…”

“…At very low z, a high level of thermal support will persist in sectors adjacent to filaments, as is apparently the case with A1795 and PKS0745-191 (see Bautz et al 2009;George et al 2009). By the same token, values > 1 will prevail in cluster sectors facing a void, causing an early onset of turbulence there given sufficienṫ M. Meanwhile, in neighboring sectors facing a filament, values ≈ 1 still hold and the thermal support may still prevail, a condition that apparently applies to A1689 (see Kawaharada et al 2010;Molnar et al 2010).…”

Strong-lensing analysis of MACS J0717.5+3745 fromHubbleFrontier Fields observations: How well can the mass distribution be constrained?

“…Actif galactic nucleus feedback can also contribute to the flattening of the central region (Martizzi et al 2012), but once again this mechanism is efficient only on small scales (up to 10-15 kpc). On scales of 100 kpc, large cores may result from violent interactions related to merging events in this actively evolving cluster, although several studies find that DM profiles are not strongly altered by a collision (Ricker & Sarazin 2001;Dekel et al 2003;Molnar et al 2010). Finally, heating of massive galaxies by dynamical friction against the diffuse dark matter distribution of the cluster can flatten the slope of the DM density profile, and sometimes even dominate over adiabatic contraction (see, e.g.…”

CLUMP-3D: three-dimensional lensing and multi-probe analysis of MACS J1206.2−0847, a remarkably regular cluster

“…Neglecting the contribution from bulk and/or turbulent motions can systematically bias low the Xray mass determination (Meneghetti et al 2010;Rasia et al 2012). High resolution cosmological simulations showed that the contribution can be significant in the core of relaxed clusters too (Lau, Kravtsov & Nagai 2009;Molnar et al 2010).…”