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

Abstract

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 r200(r200≃ 1.7 Mpc ≃ 15 arcmin). The temperature is found to decrease by roughly 70 per cent from 0.3 to 1r200. 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.

Nonthermal support for the outer intracluster medium

“…We found a value a ≈ 0 at r ≈ R/2 and values a ≈ −2 at R (as illustrated in Fig. 1 of Lapi et al 2010), consistently with the data by Bautz et al (2009) and George et al (2009).…”

“…On the other hand, environmental (even anisotropic) variance is introduced when the residual energy flowṀ v 2 2 , strongly dependent on , is modulated by the adjacent filament/void structure. At very low z, a high level of thermal support will persist in sectors adjacent to filaments, as is apparently the case with A1795 and PKS0745-191 (see Bautz et al 2009;George et al 2009). By the same token, values > 1 will prevail in cluster sectors facing a void, causing an early onset of turbulence there given sufficienṫ M. Meanwhile, in neighboring sectors facing a filament, values ≈ 1 still hold and the thermal support may still prevail, a condition that apparently applies to A1689 (see Kawaharada et al 2010;Molnar et al 2010).…”

“…Several observations (in particular with the Suzaku satellite, see George et al 2009;Bautz et al 2009;Hoshino et al 2010;Kawaharada et al 2010) support the notion that HE may be contributed by nonthermalized, turbulent motions occurring on scales of several 10 2 kpc inwards of R. On the other hand, several simulations resolve a variety of shocks in and around clusters (e.g., Ricker & Sarazin 2001;Markevitch & Vikhlinin 2007;Skillman et al 2008;Vazza et al 2010).…”

X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories

“…They find that the temperature profile between 0.3 and 1.0r 200 is consistent with a drop of 0.6, as predicted by simulations. The first temperature, density, and entropy profiles beyond r 200 were reported for another rich, massive cooling core cluster PKS 0745-191 (George et al 2009). Between 0.3 and 1r 200 they measure an average temperature drop of ∼70%.…”

“…From time to time major merger events happen in this accretion process, where two larger systems are attracted to each other and merge violently. These cluster (George et al 2009) mergers have always been very attractive study objects (see, e.g. Feretti et al 2002, for a review).…”