Abundance Profiles in Cooling-Core Clusters: a Fossil Record of Past AGN-driven Convection?

Central peaks in the iron abundance of intracluster plasma are a common feature of cooling-core galaxy clusters. Although they are centrally localized, these abundance peaks have a broader profile than the stars of the brightest cluster galaxy (BCG) that produce the excess iron, indicating that metal-enriched plasma is transported out of the BCG by some process such as turbulent diffusion. The AGN-driven convection model of Chandran & Rasera predicts the turbulent velocity profile in a steady state cluster in which radiative cooling is balanced by heating from AGN-driven convection and thermal conduction. We use the velocity profiles from this model as input into an advection/diffusion model for the transport of metals in the intracluster medium. We compare the results of our model to XMM-Newton and Chandra observations of eight clusters. Assuming a constant turbulence level over a cluster's lifetime equal to the present value, the turbulent velocities in the model can explain the observed abundance profiles in only five of the eight clusters. However, we go on to develop an analytic fit of the turbulent velocity profile as a function of the AGN power. We then deduce for each cluster the average AGN power (during the past ~10 Gyr) required to match the abundance profiles. The required average values are between 10⁴³ and 2 × 10⁴⁴ erg s^-1, while the present AGN powers span a much larger range. Our results suggest that AGN-driven convection can account for the observed abundance profiles if the AGN power varies in time with average values in the above-quoted range.