  We investigate the detection of Cool Cores (CCs) in the distant galaxy
cluster population, with the purpose of measuring the CC fraction out to
redshift 0.7 < z < 1.4. Using a sample of nearby clusters spanning a wide range
of morphologies, we define criteria to characterize cool cores, which are
applicable to the high redshift sample. We analyzed azimuthally averaged
surface brightness (SB) profiles using the known scaling relations and fitted
single/double beta models to the data. Additionally, we measured a surface
brightness concentration, c_SB, as the ratio of the peak over the ambient SB.
To verify that this is an unbiased parameter as a function of redshift, we
developed a model independent "cloning" technique to simulate the nearby
clusters as they would appear at the same redshifts and luminosities as those
in the distant sample. A more physical parameterization of CC presence is
obtained by computing the cooling time at a radius of 20 kpc from the cluster
center. The distribution of the SB concentration and the stacked radial
profiles of the low-z sample, combined with published information on the CC
properties of these clusters, show 3 degrees of SB cuspiness: non-CC, moderate
and strong CC. The same analysis applied to the high-z clusters reveals two
regimes: non-CC and moderate CC. The cooling time distribution corroborates
this result by showing a strong negative correlation with c_SB. Our analysis
indicates a significant fraction of distant clusters harboring a moderate CC
out to z=1.4, similar to those found in the local sample. The absence of strong
cooling which we report is likely linked with a higher merger rate expected at
redshift z > 0.7, and should also be related with the shorter age of distant
clusters, implying less time to develop a cool core.
