  From clusters to groups of galaxies, the powerful bremsstrahlung radiation
L_X emitted in X rays by the intracluster plasma is observed to decline sharply
with lowering virial temperatures T (i.e., at shallower depths of the
gravitational wells) after a steep local L_X-T correlation; this implies
increasing scarcity of diffuse baryons relative to dark matter, well under the
cosmic fraction. We show how the widely debated issue concerning these `missing
baryons' is solved in terms of the thermal and/or dynamical effects of the
kinetic (at low redshifts z) and radiative (at high z) energy inputs from
central active galactic nuclei, of which independent evidence is being
observed. From these inputs we compute shape and z-evolution expected for L_X-T
correlation which agree with the existing data, and provide a predictive
pattern for future observations.
