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

Abstract

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 ≲ z ≲ 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 γ′ very close to isothermal (〈γ′〉 = 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 |δ| ≤ 0.16 and (v) the physical distinction among slow and fast rotators, quantified by the v/σ ratio and the intrinsic angular momentum, is already present at z ≳ 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. © 2009 RAS.