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 M _ { \textrm { \tiny { vir } } } \gtrsim 6 \times 10 ^ { 12 } M _ { \odot } 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 - M _ { \textrm { \tiny { vir } } } relation is consistent with the X-ray analysis , extending towards lower virial masses , covering the range from ~ { } 4 \times 10 ^ { 11 } M _ { \odot } up to 5 \times 10 ^ { 12 } M _ { \odot } .
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 .