Are over-massive haloes of ultra-diffuse galaxies consistent with extended MOND?

Abstract

Aims. A sample of Coma cluster ultra-diffuse galaxies (UDGs) are modelled in the context of extended modified Newtonian dynamics (EMOND) with the aim to explain the large dark matter-like effect observed in these cluster galaxies. Methods. We first built a model of the Coma cluster in the context of EMOND using gas and galaxy mass profiles from the literature. Assuming that the dynamical mass of the UDGs satisfies the fundamental manifold of other ellipticals and that the UDG stellar mass-to-light ratio matches their colour, we then verified the EMOND formulation by comparing two predictions of the baryonic mass of UDGs. Results. We find that EMOND can explain the UDG mass, within the expected modelling errors, if they lie on the fundamental manifold of ellipsoids, but given that measurements show one UDG lying off the fundamental manifold, observations of more UDGs are needed to confirm this assumption.