By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters,we find that in 31 sample systems there exists a significant central (R≤10 h-1 71 kpc) gas entropy excess (△K0),which corresponds to ≈0.1-0.5 keV per gas particle,beyond the power-law model that best fits the radial entropy profile of the outer regions.We also find a distinct correlation between the central entropy excess △K0 and K-band luminosity L K of the central dominating galaxies (CDGs),which is scaled as △K0 ∝ LK1.6±0.4,where L K is tightly associated with the mass of the supermassive black hole hosted in the CDG.In fact,if an effective mass-to-energy conversionefficiency of 0.02 is assumed for the accretion process,the cumulative AGN feedback E AGN feedback ≈ηMBHc2 yields an extra heating of ≈0.5-17.0 keV per particle,which is sufficient to explain the central entropy excess.In most cases,the AGN contribution can compensate the radiative loss of the X-ray gas within the cooling radius (≈0.002-2.2 keV per particle),and apparently exceeds the energy required to cause the scaling relations to deviate from the self-similar predictions (≈0.2-1.0 keV per particle).In contrast to the AGN feedback,the extra heating provided by supernova explosions accounts for ≈0.01-0.08 keV per particle in groups and is almost negligible in clusters.Therefore,the observed correlation between △K0 and LK can be considered as direct evidence for AGN feedback in galaxy groups and clusters.
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