Dark matter halos of massive elliptical galaxies at $z \sim 0.2$ are
  well described by the Navarro-Frenk-White profile
  We investigate the internal structure of elliptical galaxies at $z\sim 0.2$
from a joint lensing-dynamics analysis. We model Hubble Space Telescope images
of a sample of 23 galaxy-galaxy lenses selected from the Sloan Lens ACS (SLACS)
survey. Whereas the original SLACS analysis estimated the logarithmic slopes by
combining the kinematics with the imaging data, we estimate the logarithmic
slopes only from the imaging data. We find that the distribution of the
lensing-only logarithmic slopes has a median $2.08\pm0.03$ and intrinsic
scatter $0.13 \pm 0.02$, consistent with the original SLACS analysis. We
combine the lensing constraints with the stellar kinematics and weak lensing
measurements, and constrain the amount of adiabatic contraction in the dark
matter (DM) halos. We find that the DM halos are well described by a standard
Navarro-Frenk-White halo with no contraction on average for both of a constant
stellar mass-to-light ratio ($M/L$) model and a stellar $M/L$ gradient model.
For the $M/L$ gradient model, we find that most galaxies are consistent with no
$M/L$ gradient. Comparison of our inferred stellar masses with those obtained
from the stellar population synthesis method supports a heavy initial mass
function (IMF) such as the Salpeter IMF. We discuss our results in the context
of previous observations and simulations, and argue that our result is
consistent with a scenario in which active galactic nucleus feedback
counteracts the baryonic-cooling-driven contraction in the DM halos.
