New constraints on modified Newtonian dynamics from galaxy clusters

We revisit the application of modified Newtonian dynamics (MOND) to galaxy clusters. We confront the high-quality X-ray data for eight clusters of galaxies observed by the XMM-Newton satellite with the predictions of MOND. We obtain a ratio of the MOND dynamical mass to the baryonic mass of M-m/M-b= 4.94 +/- 0.50 in the outer parts (i.e. r similar to 0.5R(vir)), in the concordance cosmological model where the predicted asymptotic ratio, if any baryons are present, is 7.7(-1.1)(+1.4) (at r >= 0.3R(vir)). We confirm that the MOND paradigm lowers the discrepancy between the binding mass and the baryonic mass in clusters by a factor of similar to 1.6 at about half the virial radius. However, at this radius about 80 per cent of the mass is still missing, and as pointed out by Sanders, this necessitates a component of dark baryons or neutrinos in the cluster core. Concerning the neutrino hypothesis, application of the new data requires a minimum neutrino mass of m(nu) > 1.74 +/- 0.34 eV to fill this gap. The corresponding 2 sigma lower limit of m(nu) > 1.06 eV is marginally inconsistent with the current constraints from the cluster number counts, and from the cosmic microwave background and large-scale structure data. MOND must invoke neutrinos to represent the main component that account for the missing mass problem in clusters.