We present results of four-pointing Suzaku X-ray observations (total ∼200 ks) of the intracluster medium (ICM) in the Abell 1835 galaxy cluster (kT ∼ 8 keV, z = 0.253) out to the virial radius (r vir ∼ 2.9 Mpc) and beyond. Faint X-ray emission from the ICM out to r vir is detected. The temperature gradually decreases with radius from ∼8 keV in the inner region to ∼2 keV at r vir . The entropy profile is shown to flatten beyond r 500 , in disagreement with the r 1.1 dependence predicted from the accretion shock heating model. The thermal pressure profile in the range 0.3r 500 < ∼ r < ∼ r vir agrees well with that obtained from the stacked Sunyaev-Zel'dovich effect observations with the Planck satellite. The hydrostatic mass profile in the cluster outskirts (r 500 < ∼ r < ∼ r vir ) falls well short of the weak lensing one derived from Subaru/Suprime-Cam observations, showing an unphysical decrease with radius. The gas mass fraction at r vir defined with the lensing total mass agrees with the cosmic baryon fraction from the WMAP 7-year data. All these results indicate, rather than the gas-clumping effect, that the bulk of the ICM in the cluster outskirts is far from hydrostatic equilibrium and infalling matter retained some of its kinetic energy. Finally, combining with our recent Suzaku and lensing analysis of Abell 1689, a cluster of similar mass, temperature, and redshift, we show that the cluster temperature distribution in the outskirts is significantly correlated with the galaxy density field in the surrounding large-scale environment at (1-2)r vir .

We report Suzaku observations of the northern half of the Hydra A cluster out to ∼ 1.4 Mpc, reaching the virial radius. This is the first Suzaku observations of a medium-size (kT ∼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 that 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 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 ∼ 2 r 500 . Beyond r 500 , the ratio of gas mass to 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 hydrostatic equilibrium at cluster outskirts. We derived radial profiles of the gas-mass-to-light ratio and 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.