ИСТИНА

The rotation curve mass-modelling represents the popular method to evaluate the parameters of both disc and dark halo, despite the fact that it has problems. We examined the reliability of its results for pseudoisothermal, Burkert and NFW dark halos. We considered two variants of models: in the first one the mass-to-light ratios of disc and bulge were taken as free parameters, in the second one we fixed them in a narrow range. The reliability of the estimates of the dark halo parameters depends on the shape and the extension of rotation curve and on the availability of detailed data for the central parts of the rotation curves. We also made tests showing how the parameters of halo change in the cases of a lack of kinematic data in the central or peripheral areas and for different spatial resolutions. From our analysis it follows that disc-halo conspiracy can be realized for the set of different pairs of DM parameters, corresponding, however, to the small variation of the dark halo mass within optical borders. We showed that due to the degeneracy between the central densities ρ0 and the radial scales Rs of the dark haloes there are considerable uncertainties of their concentrations and column density estimates. The problem is not solved by fixing the density of baryonic matter.