Kinematic constraints on the stellar and dark matter content of spiral and S0 galaxies

Abstract

(Abridged) We present mass models of a sample of 14 spiral and 14 S0 galaxies that constrain their stellar and dark matter content. For each galaxy we derive the stellar mass distribution from near-infrared photometry under the assumptions of axisymmetry and a constant Ks-band stellar mass-to-light ratio, (M/L)_Ks. To this we add a dark halo assumed to follow a spherically symmetric NFW profile and a correlation between concentration and dark mass within the virial radius, M_DM. We solve the Jeans equations for the corresponding potential under the assumption of constant anisotropy in the meridional plane, beta_z. By comparing the predicted second velocity moment to observed long-slit stellar kinematics, we determine the three best-fitting parameters of the model: (M/L)_Ks, M_DM and beta_z. These simple axisymmetric Jeans models are able to accurately reproduce the wide range of observed stellar kinematics, which typically extend to ~2-3 Re or, equivalently, ~0.5-1 R_25. We find a median stellar mass-to-light ratio at Ks-band of 1.09 (solar units) with an rms scatter of 0.31. We present preliminary comparisons between this large sample of dynamically determined stellar mass-to-light ratios and the predictions of stellar population models. The stellar population models predict slightly lower mass-to-light ratios than we measure. The mass models contain a median of 15 per cent dark matter by mass within an effective radius Re, and 49 per cent within the optical radius R_25. Dark and stellar matter contribute equally to the mass within a sphere of radius 4.1 Re or 1.0 R_25. There is no evidence of any significant difference in the dark matter content of the spirals and S0s in our sample.