Decomposition of the Visible and Dark Matter Mass Profiles in the Einstein Ring 0047-2808

Abstract

Using our semi-linear inversion method, we measure the mass profile of the lens galaxy in the Einstein ring system 0047-2808. The lens is modelled as a baryonic component following the observed light, embedded in a dark matter generalised NFW halo. The semi-linear method makes full use of the information content in the ring image. We determine an unevolved B-band mass to light ratio for the baryons of 3.05 +0.45 -0.86 h_65 M_sol/L_sol (95% CL), accounting for 65% of the total projected mass within the radius of 1.16'' traced by the ring. This result is obtained without need of dynamical measurements. The inner logarithmic slope of the halo is found to be 0.87 +0.69 -0.61 (95% CL). We find that the halo is fairly well aligned with the light but has only half the ellipticity.