Luminous Vs. dark matter in the inner parts of bright spiral galaxies

The inner part of the rotation curve is crucial in determining the nature of the dark matter. The shape of the dark spherical halo is determined by the central density and the core radius. Haloes built up by hierarchical merging in dark matter cosmogonies are cusped and dominated by dark matter at the very centre. These characteristics seem to disagree with a number of observations. The number of subhaloes around typical galaxies, as identified by satellite galaxies, is an order of magnitude smaller than predicted by cold dark matter (CDM). The observed rotation curves of dwarf and low surface brightness galaxies seem to indicate that their dark matter haloes have a constant density core instead of steep cusps. For high surface brightness galaxies, the situation is not clear and there is not consensus to whether bright galaxies are dark matter dominated at there very centres or not. We are carrying out a project to test whether the luminous mass in the inner parts of spiral galaxies can account for their observed gas kinematics or whether an additional dark matter component with a distinct mass distribution is required. For this purpose we are modelling the galaxy dynamics of a significant sample of barred spiral galaxies by running a serial 3-D composite N-body/hydrocode based on a code developed by the Geneva Observatory galactic dynamics group, on the luminous underlying matter distribution of the sample galaxies. This luminous matter distribution is obtained taking into account projection,extinction and population effects of the composite (optical-IR) images of the galaxies. We are then comparing the modelled position-velocity diagrams to the observed optical rotation curves.