AnASCAStudy of the Heavy‐Element Distribution in Clusters of Galaxies

Publisher Website
Google Scholar
Abstract
We perform a spatially resolved X-ray spectroscopic study of a set of 11 relaxed clusters of galaxies observed by the ROSAT/PSPC and ASCA/SIS. Using a method, which corrects for the energy-dependent effects of the ASCA point-spread function based on ROSAT images, we constrain the spatial distribution of Ne, Si, S, and Fe in each cluster. Theoretical prescriptions for the chemical yields of Types Ia and II supernovae then allow determination of the Fe enrichment from both types of supernovae as a function of radius within each cluster. Using optical measurements from the literature, we also determine the iron mass-to-light ratio (IMLR) separately for Fe synthesized in both types of supernovae. For clusters with the best photon statistics, we find that the total Fe abundance decreases significantly with radius while the Si abundance is either flat or decreases less rapidly, resulting in an increasing Si/Fe ratio with radius. This result indicates a greater predominance of Type II supernova (SN) enrichment at large radii in clusters. On average, the IMLR synthesized within Type II SNe increases with radius within clusters, while the IMLR synthesized within Type Ia SNe decreases. At a fixed radius of 0.4 Rvirial there is also a factor of 5 increase in the IMLR synthesized by Type II SNe between groups and clusters. This suggests that groups expelled as much as 90% of the Fe synthesized within Type II SNe at early times. All of these results are consistent with a scenario in which the gas was initially heated and enriched by Type II SN-driven galactic winds. Because of the high entropy of the preheated gas, SN II products are only weakly captured in groups. Gravitationally bound gas was then enriched with elements synthesized by Type Ia supernovae as gas-rich galaxies accreted onto clusters and were stripped during passage through the cluster core via density-dependent mechanisms (e.g., ram pressure ablation, galaxy harassment, etc.). We suggest that the high Si/Fe ratios in the outskirts of rich clusters may arise from enrichment by Type II SNe released to the intracluster medium via galactic starburst-driven winds. Low S/Fe ratios observed in clusters suggest metal-poor galaxies as a major source of SN II products.