The modified Newtonian dynamics Fundamental Plane

Abstract

Modified Newtonian dynamics (MOND) has been shown to be able to fit spiral galaxy rotation curves as well as giving a theoretical foundation for empirically determined scaling relations, such as the Tully-Fisher law, without the need for a dark matter halo. As a complementary analysis, one should investigate whether MOND can also reproduce the dynamics of early-type galaxies (ETGs) without dark matter. As a first step, we here show that MOND can indeed fit the observed central velocity dispersion σ0 of a large sample of ETGs assuming a simple MOND interpolating functions and constant anisotropy. We also show that, under some assumptions on the luminosity dependence of the Sérsic n parameter and the stellar mass-to-light ratio (M/L), MOND predicts a Fundamental Plane for ETGs: a loglinear relation among the effective radius Reff, σ0 and the mean effective intensity 〈Ie〉. However, we predict a tilt between the observed and the MOND Fundamental Planes. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.