To assess the effect of baryonic “ pinching ” of galaxy cluster dark matter ( DM ) haloes , cosmological ( \Lambda CDM ) TreeSPH simulations of the formation and evolution of two galaxy clusters have been performed , with and without baryons included .

The simulations with baryons invoke star formation , chemical evolution with non-instantaneous recycling , metallicity dependent radiative cooling , strong star-burst , driven galactic super-winds and the effects of a meta-galactic UV field , including simplified radiative transfer .
The two clusters have T \simeq 3 and 6 keV , respectively , and , at z \sim 0 , both host a prominent , central cD galaxy .

Comparing the simulations without and with baryons , it is found for the latter that the inner DM density profiles , r \la 50-100 kpc , steepen considerably : \Delta \alpha \sim 0.5-0.6 , where - \alpha is the logarithmic DM density gradient .
This is primarily due to the central stellar cDs becoming very massive , as a consequence of the onset of late time cooling flows and related star formation .
Once these spurious cooling flows have been corrected for , and the cluster gravitational potentials dynamically adjusted , much smaller pinching effects are found : \Delta \alpha \sim 0.1 .
Including the effects of baryonic pinching , central slopes of \alpha \simeq 1.0 and 1.2 are found for the DM in the two clusters , interestingly close to recent observational findings for galaxy cluster Abell 1703 based on strong gravitational lensing .

For the simulations with baryons , the inner density profile of DM and cluster gas ( ICM ) combined is found to be only very marginally steeper than that of the DM , \Delta \alpha \la 0.05 .
However , the total matter inner density profiles are found to be \Delta \alpha \sim 0.5 steeper than the inner profiles in the dark matter only simulations .