On the nature of the missing mass of galaxy clusters in MOND: the view from gravitational lensing

TL;DR

This study uses gravitational lensing data from the CLASH survey to analyze the residual missing mass in galaxy clusters under MOND, revealing a consistent density profile and potential models for the residual mass distribution.

Contribution

It provides detailed characterization of the residual missing mass profile in galaxy clusters within MOND using lensing data, and suggests models that fit the observed density profiles.

Findings

Residual missing mass density profile has an inner constant core and a steep outer slope.

A 'dark mass-follows-gas' profile with exponential cut-off fits the data well.

Inner missing-to-gas density ratio is approximately 10 across clusters.

Abstract

Modified Newtonian Dynamics (MOND) has long been known to fail in galaxy clusters, implying a residual missing mass problem for clusters in this context. Here, using mass profiles derived from strong- and weak-lensing shear, as well as magnification data, for a sample of clusters from the CLASH survey, we characterize the density profile of this residual MOND missing mass in the central Mpc of galaxy clusters. In line with results obtained in the literature from the hydrostatic equilibrium of hot gas, we find that an inner constant density core and an outer power-law slope sharper than $-3.5$ provides a good description within $\sim 1$~Mpc. We also show that the data in the central parts of clusters can be even better represented by a `dark mass-follows-gas' profile with an exponential cut-off. Clusters in the sample display a remarkable uniformity for the missing-to-hot-gas density ratio in the inner parts, of order $\sim$10, as well as for the exponential cut-off radius, of order $\sim 400$~kpc. These lensing results can in principle serve as a crucible for relativistic theories of MOND in galaxy clusters, or for any other tentative hypothesis regarding the nature of the clusters residual missing mass in the MOND context.