The SWELLS survey - IV. Precision measurements of the stellar and dark matter distributions in a spiral lens galaxy

We construct a fully self-consistent mass model for the lens galaxy SDSS J2141 at redshift 0.14, and use it to improve on previous studies by modelling its gravitational lensing effect, gas rotation curve and stellar kinematics simultaneously. We adopt a very flexible axisymmetric mass model constituted by a generalized Navarro-Frenk-White (NFW) dark matter halo and a stellar mass distribution obtained by deprojecting the multi-Gaussian expansion fit to the high-resolution K′-band laser guide star adaptive optics imaging data of the galaxy, with the (spatially constant) mass-to-light ratio as a free parameter. We model the stellar kinematics by solving the anisotropic Jeans equations. We find that the inner logarithmic slope of the dark halo is weakly constrained, i.e. , and consistent with an unmodified NFW profile; we can conclude, however, that steep profiles (γ≥ 1.5) are disfavoured (