Feedback Heating in Cluster and Galactic Cooling Flows

Abstract

Cluster cooling flow models that include both thermal conduction and AGN heating have lower overall mass cooling rates and simultaneously sustain density and temperature profiles similar to those observed with no ad hoc mass dropout. To achieve this agreement, the thermal conductivity must be about 0.35 +/- 0.10 of the Spitzer value, similar to that advocated by Narayan & Medvedev. However, when applied to galaxy/group scales the synergistic combination of AGN heating and conduction is less satisfactory. When the computed density profile and the global cooling rate are lowered by AGN heating to match observations of these smaller scale flows, the gas temperatures within about 10 kpc are too large. In addition, best-fitting flows in galaxy/groups with AGN heating and thermal conduction require larger conductivities, about 0.5 - 1.0 of the Spitzer value. When the gas density in galaxy/group flows is lowered by heating, the iron enrichment by Type Ia supernovae is more effective and the hot gas iron abundance greatly exceeds observed values. Consequently, galactic/group flows with central heating and conduction require an additional process that removes the iron: failure of Type Ia ejecta to go into the hot phase, selective cooling, etc.