Distribution of Si, Fe, and Ni in the Intracluster Medium of the Coma Cluster

We studied the distributions of Si, Fe, and Ni in the intracluster medium (ICM) of the Coma cluster, one of the largest clusters in the nearby universe, using XMM-Newton data up to 0.5 r₁₈₀ and Suzaku data of the central region up to 0.16 r₁₈₀. Using the flux ratios of the Lyα line of H-like Si and the 7.8 keV line blend to the Kα line of He-like Fe, the abundance ratios of Si to Fe and Ni to Fe of the ICM were derived using APEC model v2.0.1. The Si / Fe ratio in the ICM of the Coma cluster shows no radial gradient. The emission-weighted averages of the Si / Fe ratio in the ICM within 0.0-0.2 r₁₈₀, 0.2-0.5 r₁₈₀, and 0.0-0.5 r₁₈₀ are 0.97±0.11, 1.05±0.36, and 0.99±0.13, respectively, in solar units using the solar abundance table by Lodders (2003, ApJ, 591, 1220). These values are close to those of smaller clusters and groups of galaxies. Using the Suzaku data of the central region, the derived Ni/Fe ratio of the ICM is 0.6-1.5 in solar units, according to the same solar abundance table. The systematic difference in the derived abundance ratios by different plasma codes are about 10%. Therefore, for the ICM in the Coma cluster, the abundance pattern of Si, Fe, and Ni is consistent with the same mixture of the yields of supernova (SN) II and SN Ia in our Galaxy. Within 0.5 r₁₈₀, the cumulative iron mass-to-light ratio increases with radius, and its radial profile is similar to those of relaxed smaller clusters with cD galaxies at their center. Using the observed Si/Fe ratio, the cumulative metal mass-to-light ratios at 0.5r₁₈₀ are compared with theoretical expectations.