2002A&A...390...27A

We report on a 20ks XMM observation of the distant cluster RX J1120.1+4318, discovered at z=0.6 in the SHARC survey. The cluster has a regular spherical morphology, suggesting it is in a relaxed state. The combined fit of the EPIC/MOS and pn camera gives a cluster mean temperature of kT=5.3±0.5keV with an iron abundance of 0.47±0.19. The temperature profile, measured for the first time at such a redshift, is consistent with an isothermal atmosphere up to half the virial radius. The surface brightness profile, measured nearly up to the virial radius, is well fitted by a β-model, with β=0.78^+0.06_–0.04 and a core radius of θ_c=0.44^+0.06_–0.04 arcmin. We compared the properties of RX J1120.1+4318 with the properties of nearby clusters for two cosmological models: an Einstein-de Sitter Universe and a flat low density Universe with Ω₀=0.3. For both models, the scaled emission measure profile beyond the core, the gas mass fraction and luminosity are consistent with the expectations of the self-similar model of cluster formation, although a slightly better agreement is obtained for a low density Universe. There is no evidence of a central cooling flow, in spite of the apparent relaxed state of the cluster. This is consistent with its estimated cooling time, larger than the age of the Universe at the cluster redshift. The entropy profile shows a flat core with a central entropy of ∼140keV.cm², remarkably similar to the entropy floor observed in nearby clusters, and a rising profile beyond typically 0.1 virial radius. Implications of our results, in terms of non-gravitational physics in cluster formation, are discussed.