Physical cool-core condensation radius in massive galaxy clusters

We investigate the properties of cool cores in an optimally selected sampleof 37 massive and X-ray-bright galaxy clusters, with regular morphologies,observed with Chandra. We measured the density, temperature, and abundanceradial profiles of their intracluster medium (ICM). From these independentquantities, we computed the cooling (tcool) free-fall (tff), and turbulence(teddy) timescales as a function of radius. By requiring the profile-crossingcondition, tcool=teddy=1, we measured the cool-core condensation radius Rccc,within which the balancing feeding and feedback processes generate theturbulent condensation rain and related chaotic cold accretion (CCA). We alsoconstrained the complementary (quenched) cooling flow radius Rqcf, obtained viathe condition tcool=25Xtff, that encompasses the region of thermally unstablecooling. We find that in our cluster sample and in the limited redshift rangeconsidered (1.3E14<16.6E14 Msun, 0.03<0.29), the distribution of Rcccpeaks at 0.01r500 and the entire range remains below 0.07r500, with a very weakincrease with redshift and no dependence on the cluster mass. We find that Rqcfis typically 3 times larger than Rccc, with a wider distribution, and growingmore slowly along Rccc, according to an average relation Rqcf~Rccc^(0.46), witha large intrinsic scatter. We suggest that this sublinear relation can beunderstood as an effect of the micro rain of pockets of cooled gas flickeringin the turbulent ICM, whose dynamical and thermodynamical properties arereferred to as "macro weather". Substituting the classical cool-core radiusR(7.7Gyr), we propose that Rqcf is an indicator of the size of the global corestied to the long-term macro weather, with the inner Rccc closely tracing theeffective condensation rain and chaotic cold accretion (CCA) zone that feedsthe central supermassive black hole.