0256 . 5 + 0006 : a merging cluster of galaxies at z = 0 . 36 observed with Xmm – newton

We present here a study based on Xmm–newton data of RX J0256.5+0006, a medium distant (z=0.36) cluster of galaxies found in the Bright SHARC catalog. The X-ray emitting intracluster medium shows a bimodal structure: one main cluster component and a substructure in the west, which very likely falls onto the main cluster centre. The subcluster shows after subtraction of the main cluster component a cometary shape pointing away from the main cluster centre, suggesting that ram pressure stripping is at work. Despite the indication of interaction between the two components we surprisingly do not find any sign of temperature gradients, which is contradictory to predictions from hydro dynamical simulations of cluster mergers. Due to the non-symmetric form of the main cluster we extract three surface brightness profiles in different sectors around its centre. We see large variations between the profiles, which we quantify by β model fitting. The corresponding rc's vary between 0.1-0.5 Mpc and the β's between 0.5–1.2. The variations of the profiles and the β model parameters indicate that the main cluster is not entirely relaxed. This hypothesis is strengthened further by the fact that the cluster is over luminous with respect to the (z-evolving) Lx − T relation found for nearby clusters. Galaxy clusters show a high degree of self-similarity. Comparing our profiles to the scaled reference emission measure profile of Arnaud et al. based on nearby clusters, we find that only the profile extracted northeast (NE) of the main cluster centre is similar to this reference profile. This indicates that only the NE profile is representative for the relaxed part of this cluster component. Based on the β model parameters of the NE profile and the spectroscopically fitted temperature of kT = 4.9 +0.5 −0.4 keV we find for the total mass within r500 using the hydrostatic approach M500 ∼ 4 × 10 14 M⊙ for the main cluster component. This value is in good agreement with the value (M500 = 3.9 × 10 14 M⊙) obtained using the z-evolving M500 − T relation from the HIFLUGCS sample based on nearby clusters. A non-z-evolving M − T relation is only marginally consistent with our result. This is an indication that there exists evolution in the M − T relation, as predicted from simple scaling laws. Calculating the corresponding gas mass fraction we find fg ∼ 18 − 20% which is in good agreement with other work. …