Suzaku Observation of the Metallicity Distribution in the Intracluster Medium of the Fornax Cluster(Chapter 3. Chemical Structure and Evolution Clusters of Galaxy, The Extreme Universe in the Suzaku Era)

The metallicity distribution in the Fornax cluster was studied with the XIS instrument on board the Suzaku satellite. The K-shell lines of O and Mg were resolved clearly, and the abundances of O, Mg, Si, S, and Fe were measured with great accuracy. The region within a 4 � radius of NGC 1399 shows approximately solar abundances of Fe, Si, and S, while the O/Fe and Mg/Fe abundance ratios are about 0.4–0.5 and 0.7 in solar units, respectively. In the outer region of the radius range 6 � <r< 23 � , the Fe and Si abundances drop to 0.4–0.5 solar and show no significant gradient within this region. The abundance ratios, O/Fe and Mg/Fe, are consistent with those in the central region. We also measured the Fe abundance around NGC 1404 to be approximately solar, and the O, Ne, and Mg abundances to be 0.5–0.7 times the Fe level. A significant relative enhancement of Fe within 130kpc of NGC 1399 and in NGC 1404 indicates an origin in SN Ia, in contrast to the species O, Ne, and Mg, which reflect the stellar metallicity. The mass-to-light ratios for O and Fe within 130kpc of NGC 1399 are over an order of magnitude lower than those in rich clusters, reflecting the metal enrichment history of this poor cluster.