On the average density profile of dark-matter halos in the inner regions
  of massive early-type galaxies
  We study a sample of 39 massive early-type lens galaxies at redshift z < 0.3
to determine the slope of the average dark-matter density profile in the
innermost regions. We keep the strong lensing and stellar population synthesis
modeling as simple as possible to measure the galaxy total and luminous masses.
By rescaling the values of the Einstein radius and dark-matter projected mass
with the values of the luminous effective radius and mass, we combine all the
data of the galaxies in the sample. We find that between 0.3 and 0.9 times the
value of the effective radius the average logarithmic slope of the dark-matter
projected density profile is -1.0 +/- 0.2 (i.e., approximately isothermal) or
-0.7 +/- 0.5 (i.e., shallower than isothermal), if, respectively, a constant
Chabrier or heavier, Salpeter-like stellar IMF is adopted. These results
provide positive evidence of the influence of the baryonic component on the
contraction of the galaxy dark-matter halos, compared to the predictions of
dark matter-only cosmological simulations, and open a new way to test models of
structure formation and evolution within the standard LCDM cosmological
scenario.
