Dark matter fluid constraints from galaxy rotation curves

Galaxy rotation curves are considered to be con-vincing evidence for dark matter or some dynamically equiv-alent alternative mechanism. Starting only from the rotation curve data, we present a model independent approach of test-ing a general hypothesis that dark matter has the properties of a barotropic fluid. It is shown how the speed of sound squared can be expressed in terms of rotation curve data and their radial derivatives and how model independent constraints can be obtained from the requirements that it is confined between 0 and c(2). Using the Milky Way rotation curve data available in the literature, we obtain the constraints on the barotropic fluid speed of sound and illustrate the potential of this approach. Technical challenges, limitations and pos-sible future extensions and improvements of the proposed approach are discussed.