Limits on the power-law mass and luminosity density profiles of elliptical galaxies from gravitational lensing systems

We use 118 strong gravitational lenses observed by the SLACS, BOSS emission-line lens survey (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 similar to 1. Assuming power-law density profiles for the total mass density, rho = rho(0)(r/r(0))(-alpha), and luminosity density, v = v(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-fitting cosmology as a prior, we find gamma = 2.132 +/- 0.055 with a mild trend partial derivative gamma/partial derivative z(1) = -0.067 +/- 0.119 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 +/- 0.031, partial derivative alpha/partial derivative z(1) = -0.121 +/- 0.078 and delta = 2.710 +/- 0.143. The model in which mass traces light is rejected at >95 per cent 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(-1) < sigma(ap) <= 300 km s(-1)) show the best consistency with the singular isothermal sphere as an effective model of galactic lenses.