MOND plus classical neutrinos not enough for cluster lensing

TL;DR

This study uses gravitational lensing to test dark matter models in galaxy clusters, finding that neutrino masses in the 2-7 eV range are incompatible with observations, challenging some MOND-based theories.

Contribution

It provides new constraints on dark matter phase space density in clusters using combined strong and weak lensing data, challenging neutrino-based explanations for MOND.

Findings

Neutrino masses of 2-7 eV are inconsistent with lensing data.

Lensing observations constrain dark matter phase space density in cluster centers.

Standard neutrino masses cannot account for the missing mass in MOND frameworks.

Abstract

Clusters of galaxies offer a robust test bed for probing the nature of dark matter that is insensitive to the assumption of the gravity theories. Both Modified Newtonian Dynamics (MOND) and General Relativity (GR) would require similar amounts of non-baryonic matter in clusters as MOND boosts the gravity only mildly on cluster scales. Gravitational lensing allows us to estimate the enclosed mass in clusters on small (20 - 50 kpc) and large (several 100 kpc) scales independent of the assumptions of equilibrium. Here we show for the first time that a combination of strong and weak gravitational lensing effects can set interesting limits on the phase space density of dark matter in the centers of clusters. The phase space densities derived from lensing observations are inconsistent with neutrino masses ranging from 2 - 7 eV, and hence do not support the 2 eV-range particles required by MOND. To survive, plausible modifications for MOND may be either an additional degree of dynamical freedom in a co-variant incarnation or mass-varying theories of neutrinos.