  We use 118 strong gravitational lenses observed by the SLACS, BELLS, LSD and
SL2S surveys to constrain the total mass profile and the profile of luminosity
density of stars (light-tracers) in elliptical galaxies up to redshift $z \sim
1$. Assuming power-law density profiles for the total mass density,
$\rho=\rho_0(r/r_0)^{-\alpha}$, and luminosity density,
$\nu=\nu_0(r/r_0)^{-\delta}$, we investigate the power law index and its first
derivative with respect to the redshift. Using Monte Carlo simulations of the
posterior likelihood taking the Planck's best-fitted cosmology as a prior, we
find $\gamma= 2.132\pm0.055$ with a mild trend $\partial \gamma/\partial z_l=
-0.067\pm0.119$ when $\alpha=\delta=\gamma$, suggesting that the total density
profile of massive galaxies could have become slightly steeper over cosmic
time. Furthermore, similar analyses performed on sub-samples defined by
different lens redshifts and velocity dispersions, indicate the need of
treating low, intermediate and high-mass galaxies separately. Allowing $\delta$
to be a free parameter, we obtain $\alpha=2.070\pm0.031$, $\partial
\alpha/\partial z_l= -0.121\pm0.078$, and $\delta= 2.710\pm0.143$. The model in
which mass traces light is rejected at $>95\%$ confidence and our analysis
robustly indicates the presence of dark matter in the form of a mass component
that is differently spatially extended than the light. In this case,
intermediate-mass elliptical galaxies ($200$ km/s $ < \sigma_{ap} \leq 300$
km/s) show the best consistency with the singular isothermal sphere as an
effective model of galactic lenses.
