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Diagnostics of baryonic cooling in lensing galaxies




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 Mvir≳ 6 × 1012 M 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 4 × 1011 up to 5 × 1012 M. 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 disfavoured, requiring additional mechanisms – such as mass loss during the contraction process – to play a role during the phases following the collapse of the haloes.