Heating, Conduction, and Minimum Temperatures in Cooling Flows

There is mounting observational evidence from Chandra for strong interactionbetween keV gas and AGN in cooling flows. It is now widely accepted that thetemperatures of cluster cores are maintained at a level of 1 keV and that themass deposition rates are lower than earlier ROSAT/Einstein values. Recenttheoretical results suggest that thermal conduction can be very efficient evenin magnetized plasmas. Motivated by these discoveries, we consider a ``doubleheating model'' which incorporates the effects of simultaneous heating by boththe central AGN and thermal conduction from the hot outer layers of clusters.Using hydrodynamical simulations, we demonstrate that there exists a family ofsolutions that does not suffer from the cooling catastrophe. In these cases,clusters relax to a stable final state, which is characterized by minimumtemperatures of order 1 keV and density and temperature profiles consistentwith observations. Moreover, the accretion rates are much reduced, therebyreducing the need for excessive mass deposition rates required by the standardcooling flow models.Comment: 7 pages, 2 figures, minor changes, accepted for The Astrophysical Journa