Substructure lensing in galaxy clusters as a constraint on low-mass sterile neutrinos in tensor-vector-scalar theory: The straight arc of Abell 2390

Abstract

Certain covariant theories of the modified Newtonian dynamics paradigm seem to require an additional hot dark matter (HDM) component -in the form of either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs) with a mass around 11eV -to be relieved of problems ranging from cosmological scales down to intermediate ones relevant for galaxy clusters. Here we suggest using gravitational lensing by galaxy clusters to test such a marriage of neutrino HDM and modified gravity, adopting the framework of tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter (CDM), such HDM is subject to strong phase-space constraints, which allows one to check cluster lens models inferred within the modified framework for consistency. Since the considered HDM particles cannot collapse into arbitrarily dense clumps and only form structures well above the galactic scale, systems which indicate the need for dark substructure are of particular interest. As a first example, we study the cluster lens Abell 2390 and its impressive straight arc with the help of numerical simulations. Based on our results, we outline a general and systematic approach to model cluster lenses in TeVeS which significantly reduces the calculation complexity. We further consider a simple bimodal lens configuration, capable of producing the straight arc, to demonstrate our approach. We find that such a model is marginally consistent with the hypothesis of 11eV SNs. Future work including more detailed and realistic lens models may further constrain the necessary SN distribution and help to conclusively assess this point. Cluster lenses could therefore provide an interesting discriminator between CDM and such modified gravity scenarios supplemented by SNs or other choices of HDM.

The Acceleration Scale, Modified Newtonian Dynamics, and Sterile Neutrinos

“…Some of the dynamical mass must be provided, as expected, by the central galaxies, but the required amount implies a mass-to-light ratio of 1.2M ⊙ /L ⊙ in the K band, in agreement with stellar population synthesis models. An 11 eV sterile neutrino is also consistent with the straight arc, originated by a strong lensing effect, observed in the cluster A2390 [49].…”

Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions

“…Again, it was shown that the density of missing mass was compatible with 2 eV ordinary neutrinos, like in most clusters with T > 4 keV [140]. Finally, let us note that strong lensing was also recently used as a robust probe of the matter distribution on scales of 100 kpc in galaxy clusters, especially in the cluster Abell 2390 [150]. A residual missing mass was again found, compatible with the densities provided by fermionic hot dark matter candidates only for masses of ∼ 10 eV and heavier.…”

Unifying all mass discrepancies with one effective gravity law?

“…1) in small galaxies and in the solar system [14]. Additionally, there will be only very mild (< 50%) variations of A 0 inside galaxies, as well as between galaxies, small variations which might be desirable to explain some anomalies in strong lensing galaxies [15][16][17][18][19]. In any case this scatter is acceptable as the MOND formula works for all galaxies as long as a 0 is within the range between 0.9 and 1.7 × 10 −10 m s −2 [13,20].…”