Suzaku Observations of the Hydra A Cluster out to the Virial Radius

Abstract

Abstract We report on Suzaku observations of the northern half of the Hydra A cluster out to $ \sim$ 1.4 Mpc, reaching the virial radius. There are the first Suzaku observations of a medium-size ($ kT$$ \sim$ 3 keV) cluster out to the virial radius. Two observations were conducted, north-west and north-east offsets, which continue in a filament direction and a void direction of the large-scale structure of the Universe, respectively. The X-ray emission and distribution of galaxies elongate in the filament direction. The temperature profiles in the two directions are mostly consistent with each other within the error bars, and drop to 1.5 keV at 1.5 $ r_{500}$ . As observed by Suzaku in hot clusters, the entropy profile becomes flatter beyond $ r_{500}$ , in disagreement with the $ r^{1.1}$ relationship, which is expected from accretion shock heating models. When scaled with the average intracluster medium (ICM) temperature, the entropy profiles of clusters observed with Suzaku are universal, and do not depend on the system mass. The hydrostatic mass values in the void and filament directions are in good agreement, and the Navarro, Frenk, and White universal mass profile represents the hydrostatic mass distribution up to $ \sim$ 2$ r_{500}$ . Beyond $ r_{500}$ , the ratio of the gas mass to the hydrostatic mass exceeds the result of the Wilkinson microwave anisotropy probe, and at $ r_{100}$ , these ratios in the filament and void directions reach 0.4 and 0.3, respectively. We discuss possible deviations from the hydrostatic equilibrium at cluster outskirts. We derived radial profiles of the gas-mass-to-light ratio and the iron-mass-to-light ratio out to the virial radius. Within $ r_{500}$ , the iron-mass-to-light ratio of the Hydra A cluster was compared with those in other clusters observed with Suzaku.