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

TL;DR

This study combines gravitational lensing and stellar dynamics to analyze six early-type galaxies at redshifts 0.08 to 0.33, revealing they are nearly isothermal, rounder than 0.65, with dark matter fractions of 15-30%, and show properties similar to local galaxies.

Contribution

First detailed combined lensing and dynamics analysis of intermediate-redshift early-type galaxies, confirming their structural and dynamical similarity to nearby counterparts.

Findings

Galaxies are well described by an isothermal power-law density profile.

Dark matter fraction within effective radius is 15-30%.

Galaxies are mildly anisotropic and show early signs of slow/fast rotator distinction.

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 (HST)/ACS high-resolution imaging and VLT 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 to 30 per cent; (iv) the sample galaxies are only mildly anisotropic, with delta <= 0.16; (v) the physical distinction among slow and fast rotators, quantified by the v/sigma 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. (Abridged)