Is There Evidence for Flat Cores in the Halos of Dwarf Galaxies? The Case of NGC 3109 and NGC 6822

We present cosmologically motivated, high resolution models for two nearby dwarf galaxies: NGC3109 and NGC6822, that present the strongest observational support for a flat core at the center of galactic dark matter halos. However, our analysis shows that the rotation curves of these two galaxies are instead quite compatible with their DM halos having steep cuspy density profiles. The rotation curves in our models are measured using standard observational techniques, projecting velocities along the line of sight of an artificial observer and performing a tilted ring analysis. The models reproduce the rotation curves of both galaxies, the disk surface brightness profiles as well as the profile of isophotal ellipticity and position angle. The models are centrally dominated by baryons; however, the dark matter component is globally dominant. The simulated disk mass is marginal consistent with a stellar mass-to-light ratio in agreement with the observed colors and the detected gaseous mass. We show that non-circular motions combined with gas pressure support and projection effects systematically underestimate by up to 50% the rotation velocity of cold gas in the central 1 kpc region, creating the illusion of a constant density core. Our results strongly suggest that there is no contradiction between the observed rotation curves in dwarf galaxies and the cuspy central dark matter density profiles predicted by the Cold Dark Matter model.