The combination of gravitational lensing and stellar dynamics breaks the mass-anisotropy degeneracy and provides stringent constraints on the distribution of luminous and dark matter in early-type ( E/S0 ) galaxies out to z \approx 1 .
We present new observations and models of three lens systems ( CFRS03.1077 , HST14176+5226 , HST15433+5352 ) and the combined results from the five field E/S0 lens galaxies at z \approx 0.5 { - } 1.0 analyzed as part of the Lenses Structure & Dynamics ( LSD ) Survey .
Our main results are : ( i ) Constant mass-to-light ratio models are ruled out at > 99 \% CL for all five E/S0 galaxies , consistent with the presence of massive and extended dark-matter halos .
The range of projected dark-matter mass fractions inside the Einstein radius is f _ { DM } =0.37–0.72 , or 0.15–0.65 inside the effective radius R _ { e } for isotropic models .
( ii ) The average effective power-law slope of the total ( luminous+dark ; \rho _ { tot } \propto r ^ { - \gamma ^ { \prime } } ) mass distribution is \langle \gamma ^ { \prime } \rangle =1.75 \pm 0.10 ( 1.57 \pm 0.16 ) for Osipkov-Merritt models with anisotropy radius r _ { i } = \infty ( R _ { e } ) with an rms scatter of 0.2 ( 0.35 ) , i.e. marginally flatter than isothermal ( \gamma ^ { \prime } = 2 ) .
The ratio between the observed central stellar velocity dispersion and that from the best-fit singular isothermal ellipsoid ( SIE ) lens model is \langle f _ { SIE } \rangle = \langle \sigma / \sigma _ { SIE } \rangle = 0.87 \pm 0.04 with 0.08 rms , consistent with flatter-than-isothermal density profiles .
Considering that \gamma ^ { \prime } > 2 and f _ { SIE } > 1 have been reported for other systems ( i.e. B1608+656 and PG1115+080 ) , we conclude that there is a significant intrinsic scatter in the slope of the mass-density profile of lens galaxies ( rms \sim 15 % ) , similar to what is found for local E/S0 galaxies .
Hence , the isothermal approximation is not sufficiently accurate for applications that depend critically on the slope of the mass-density profile , such as the measurement of the Hubble Constant from time-delays .
( iii ) The average inner power-law slope \gamma of the dark-matter halo is constrained to be \langle \gamma \rangle = 1.3 ^ { +0.2 } _ { -0.4 } ( 68 % C.L .
) , if the stellar velocity ellipsoid is isotropic ( r _ { i } = \infty ) or an upper limit of \gamma < 0.6 , if the galaxies are radially anisotropic ( r _ { i } = R _ { e } ) .
The observed range of slopes of the inner dark-matter distribution is consistent with the results from numerical simulations only for an isotropic velocity ellipsoid and if baryonic collapse and star-formation do not steepen dark-matter density profiles .
( iv ) The average stellar mass-to-light ratio evolves as d \log ( M _ { * } / L _ { B } ) / dz = -0.72 \pm 0.10 , obtained via a Fundamental Plane analysis .
An independent analysis based on lensing and dynamics gives an average \langle d \log ( M _ { * } / L _ { B } ) / dz \rangle = -0.75 \pm 0.17 .
Both values indicate that the mass-to-light ratio evolution for our sample of field E/S0 galaxies is slighly faster than those in clusters , consistent with the hypothesis that field E/S0 galaxies experience secondary bursts ( \sim 10 % in mass ) of star formation at z < 1 .
These findings are consistent with pure luminosity evolution of E/S0 galaxies in the past 8 Gyrs , and would be hard to reconcile with scenarios involving significant structural and dynamical evolution .