The XMM-NEWTON Ω project I. The X-ray luminosity-temperature relation at z > 0.4

We describe XMM-Newton Guaranteed Time observations of a sample of eight high redshift (0.45 < z < 0.62) clusters. The goal of these observations was to measure the luminosity and the temperature of the clusters to a precision of ∼10%, leading to constraints on the possible evolution of the luminosity-temperature (Lx − Tx) relation, and ultimately on the values of the matter density, ΩM, and, to a lesser extent, the cosmological constant ΩΛ. The clusters were drawn from the SHARC and 160 Square Degree (160SD) ROSAT surveys and span a bolometric (0.0-20 keV) luminosity range of 2.0 to 14.4×10 44 erg s −1 (H0 = 50, ΩM = 1, ΩΛ = 0). Here we describe our data analysis techniques and present, for the first time with XMM-Newton, a Lx − Tx relation. For each of the eight clusters in the sample, we have measured total (r < rvirial) bolometric luminosities, performed β-model fits to the radial surface profiles and made spectral fits to a single temperature isothermal model. We describe data analysis techniques that pay particular attention to background mitigation. We have also estimated temperatures and luminosities for two known clusters (Abell 2246 and RX J1325.0−3814), and one new high redshift cluster candidate (XMMU J084701.8+345117), that were detected off-axis. Characterizing the Lx −Tx relation as Lx = L6( T 6k eV ) α ,w e find L6 = 15.9 +7.6 −5.2 × 10 44 erg s −1 and α = 2.7 ± 0. 4f or anΩ Λ = 0.0, ΩM = 1.0, H0 = 50 km s −1 Mpc −1 cosmology at a typical redshift z ∼ 0.55. Comparing with the low redshift study by Markevitch (1998), we find α to be in agreement, and assuming Lx − Tx to evolve as (1 + z) A ,w e fi ndA = 0.68 ± 0.26 for the same cosmology and A = 1.52 +0.26 −0.27 for an ΩΛ = 0.7, ΩM = 0.3 cosmology. Our A values are very similar to those found previously by Vikhlinin et al. (2002) using a compilation of Chandra observations of 0.39 < z < 1.26 clusters. We conclude that there is now evidence from both XMM-Newton and Chandra for an evolutionary trend in the Lx − Tx relation. This evolution is significantly below the level expected from the predictions of the self-similar model for an ΩΛ = 0.0, ΩM = 1.0, cosmology, but consistent with self-similar model in an ΩΛ = 0.7, ΩM = 0.3 cosmology. Our observations lend support to the robustness and completeness of the SHARC and 160SD surveys.