The relationship between cooling flows and metallicity measurements for X - ray luminous clusters

We explore the relationship between the metallicity of the intracluster gas in clusters of galaxies, determined by X-ray spectroscopy, and the presence of cooling flows. Using ASCA spectra and ROSAT images, we demonstrate a clear segregation between the metallicities of clusters with and without cooling flows. On average, cooling-flow clusters have an emission-weighted metallicity a factor ∼ 1.8 times higher than that of non-cooling flow systems. We suggest this to be due to the presence of metallicity gradients in the cooling flow clusters, coupled with the sharply peaked X-ray surface brightness profiles of these systems. Non-cooling flow clusters have much flatter X-ray surface brightness distributions and are thought to have undergone recent merger events which may have mixed the central high-metallicity gas with the surrounding less metal-rich material. We find no evidence for evolution in the emission-weighted metallicities of clusters within z ∼ 0.3.