  Theoretical studies of structure formation find an inverse proportionality
between the concentration of dark matter haloes and virial mass. This trend has
been recently confirmed for virial masses Mvir > ~6e12 Msun by the observation
of the X-ray emission from the hot halo gas. We present an alternative approach
to this problem, exploring the concentration of dark matter haloes over galaxy
scales on a sample of 18 early-type systems. Our c-Mvir relation is consistent
with the X-ray analysis, extending towards lower virial masses, covering the
range from ~4e11 Msun up to 5e12 Msun. A combination of the lensing analysis
along with photometric data allows us to constrain the baryon fraction within a
few effective radii, which is compared with prescriptions for adiabatic
contraction (AC) of the dark matter haloes. We find that the standard methods
for AC are strongly disfavored, requiring additional mechanisms -- such as mass
loss during the contraction process -- to play a role during the phases
following the collapse of the haloes.
