Metallicity Gradients in the Intracluster Gas of Abell 496

摘要

Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell496 confirms there are mild metal abundance enhancements near the center, aspreviously found by White et al. (1994) in a joint analysis of Ginga LAC andEinstein SSS spectra. Simultaneous analysis of spectra from all ASCAinstruments (SIS + GIS) shows that the iron abundance is 0.36 +- 0.03 solar3-12' from the center of the cluster and rises ~50% to 0.53 +- 0.04 solarwithin the central 2'. The F-test shows that this abundance gradient issignificant at the >99.99% level. Nickel and sulfur abundances are alsocentrally enhanced. We use a variety of elemental abundance ratios to assessthe relative contribution of SN Ia and SN II to the metal enrichment of theintracluster gas. We find spatial gradients in several abundance ratios,indicating that the fraction of iron from SN Ia increases toward the clustercenter, with SN Ia accounting for ~50% of the iron mass 3-12' from the centerand ~70% within 2'. The increased proportion of SN Ia ejecta at the center issuch that the central iron abundance enhancement can be attributed wholly to SNIa; we find no significant gradient in SN II ejecta. These spatial gradients inthe proportion of SN Ia/II ejecta imply that the dominant metal enrichmentmechanism near the center is different than in the outer parts of the cluster.We show that the central abundance enhancement is unlikely to be due to rampressure stripping of gas from cluster galaxies, or to secularly accumulatedstellar mass loss within the central cD. We suggest that the additional SN Iaejecta near the center is the vestige of a secondary SN Ia-driven wind from thecD (following a more energetic protogalactic SN II-driven wind phase), whichwas partially smothered in the cD due to its location at the cluster center.