The prediction of rotation curves in gas-dominated dwarf galaxies with modified dynamics

Abstract

I consider the observed rotation curves of 12 gas-dominated low-surface-brightness galaxies-objects in which the mass of gas ranges between 2.2 and 27 times the mass of the stellar disc (mean = 9.4). This means that, in the usual decomposition of rotation curves into those resulting from various mass components, the mass-to-light ratio of the luminous stellar disc effectively vanishes as an additional adjustable parameter. It is seen that the observed rotation curves reflect the observed structure in gas surface density distribution often in detail. This fact is difficult to comprehend in the context of the dark matter paradigm where the dark halo completely dominates the gravitational potential in the low surface density systems; however it is an expected result in the context of modified Newtonian dynamics (MOND) in which the baryonic matter is the only component. With MOND the calculated rotation curves are effectively parameter-free predictions.