X-ray observations of the galaxy cluster PKS 0745−191: to the virial radius, and beyond

We measure X-ray emission from the outskirts of the cluster of galaxies PKS 0745?191 with Suzaku , determining radial profiles of density, temperature, entropy, gas fraction and mass. These measurements extend beyond the virial radius for the first time, providing new information about cluster assembly and the diffuse intracluster medium out to  ～1.5  r ₂₀₀( r ₂₀₀? 1.7 Mpc ? 15 arcmin  ). The temperature is found to decrease by roughly 70 per cent from 0.3 to  1 r ₂₀₀  . We also see a flattening of the entropy profile near the virial radius and consider the implications this has for the assumption of hydrostatic equilibrium when deriving mass estimates. We place these observations in the context of simulations and analytical models to develop a better understanding of non-gravitational physics in the outskirts of the cluster.