Missing Baryons, from Clusters to Groups of Galaxies

Abstract

From clusters to groups of galaxies, the powerful bremsstrahlung radiation LX 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 LX − 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 the LX − T correlation which agree with the existing data, and provide a predictive pattern for future observations.