Dark matter in early-type spiral galaxies: the case of NGC 2179 and of NGC 2775

Abstract

We present the stellar and ionized-gas velocity curves and velocity-dispersion profiles along the major axis for six early-type spiral galaxies. Two of these galaxies, namely NGC 2179 and NGC 2775, are particularly suited for the study of dark matter halos. Using their luminosity profiles and modeling their stellar and gaseous kinematics, we derive the mass contributions of the luminous and the dark matter to the total potential. In NGC 2179 we find that the data (measured out to about the optical radius Ropt) unambiguously require the presence of a massive dark halo. For the brighter and bigger object NGC 2775, we can rule out a significant halo contribution at radii R < 0:6Ropt. Although preliminary, these results agree with the familiar mass distribution trend known for late-type spirals of comparable mass.