Two-dimensional kinematics of SLACS lenses - II. Combined lensing and dynamics analysis of early-type galaxies at z=0.08-0.33

We present the first detailed analysis of the mass and dynamical structure of a sample of six early-type lens galaxies, selected from the Sloan Lens ACS Survey, in the redshift range 0.08 less than or similar to z less than or similar to 0.33. Both Hubble Space Telescope/Advanced Camera for Surveys (ACS) high-resolution imaging and Very Large Telescope Visible Multi-Object Spectrograph (VIMOS) integral-field spectroscopy are available for these systems. The galaxies are modelled - under the assumptions of axial symmetry and two-integral stellar distribution function - by making use of the CAULDRON code, which self-consistently combines gravitational lensing and stellar dynamics and is fully embedded within the framework of Bayesian statistics. The principal results of this study are: (i) all galaxies in the sample are well described by a simple axisymmetric power-law profile for the total density, with a logarithmic slope gamma' very close to isothermal (<gamma'> = 1.98 +/- 0.05 and an intrinsic spread close to 5 per cent) showing no evidence of evolution over the probed range of redshift; (ii) the axial ratio of the total density distribution is rounder than 0.65 and in all cases, except for a fast rotator, does not deviate significantly from the flattening of the intrinsic stellar distribution; (iii) the dark matter fraction within the effective radius has a lower limit of about 15-30 per cent; (iv) the sample galaxies are only mildly anisotropic, with vertical bar delta vertical bar <= 0.16 and (v) the physical distinction among slow and fast rotators, quantified by the nu/sigma ratio and the intrinsic angular momentum, is already present at z greater than or similar to 0.1. Altogether, early-type galaxies at z = 0.08-0.33 are found to be markedly smooth and almost isothermal systems, structurally and dynamically very similar to their nearby counterparts. This work confirms the effectiveness of the combined lensing and dynamics analysis as a powerful technique for the study of early-type galaxies beyond the local Universe.