We selected an unbiased, flux-limited and almost volume-complete sample of 13 distant, X-ray luminous (DXL, z ∼ 0.3) clusters and one supplementary cluster at z = 0.2578 from the REFLEX Survey (the REFLEX-DXL sample). We performed a detailed study to explore their X-ray properties using XMM-Newton observations. Based on the precise radial distributions of the gas density and temperature, we obtained robust cluster masses and gas mass fractions. The average gas mass fraction of the REFLEX-DXL sample at r 500 , 0.116 ± 0.007, agrees with the previous cluster studies and the WMAP baryon fraction measurement. The scaled profiles of the surface brightness, temperature, entropy, gas mass and total mass are characterized by a self-similar behaviour at radii above 0.2−0.3 r 500 . The REFLEX-DXL sample confirms the previous studies of the normalization of the scaling relations (L−T , L−M, M−T and M gas −T ) when the redshift evolution of the scaling relations is accounted for. We investigated the scatter of the scaling relations of the REFLEX-DXL sample. This gives the correlative scatter of (0.20, 0.10) for variable of (M, T ) of the M 500 −T relation, for example.
Context. The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. Aims. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z = 0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 × 10 44 h −2 70 erg s −1 in the 0.1−2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. Methods. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. Results. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. Conclusions. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications.
We present the X-ray properties and scaling relations of a flux-limited morphology-unbiased sample of 12 X-ray luminous galaxy clusters at redshift around 0.2 based on XMM-Newton observations. The scaled radial profiles are characterized by a self-similar behavior at radii outside the cluster cores (>0.2r 500 ) for the temperature (T ∝ r −0.36 ), surface brightness, entropy (S ∝ r 1.01 ), gas mass and total mass. The cluster cores contribute up to 70% of the bolometric X-ray luminosity. The X-ray scaling relations and their scatter are sensitive to the presence of the cool cores. Using the X-ray luminosity corrected for the cluster central region and the temperature measured excluding the cluster central region, the normalization agrees to better than 10% for the cool core clusters and non-cool core clusters, irrelevant to the cluster morphology. No evolution of the X-ray scaling relations was observed comparing this sample to the nearby and more distant samples. With the current observations, the cluster temperature and luminosity can be used as reliable mass indicators with the mass scatter within 20%. Mass discrepancies remain between X-ray and lensing and lead to larger scatter in the scaling relations using the lensing masses (e.g. ∼40% for the luminosity-mass relation) than using the X-ray masses (<20%) due to the possible reasons discussed.
We carry out a two-dimensional study of temperature, entropy, and pressure distributions in a nearly volume-limited subsample of REFLEX clusters at redshift 0.3, the REFLEX-DXL. We use the observations gained by XMM-Newton, which cover the central 1−2 × r 500 . We define the substructure in both entropy and pressure as a deviation from the mean profile of the sample. The non-parametric locally weighted regression suggests a broken power-law approximation to the entropy profile with inner and outer slopes of 0.78 and 0.52, respectively, and a break at 0.5r 500 . Characterization of the pressure profile is more complex, requiring three power laws, with slopes −0.64 at r < 0.3r 500 , −2.47 at r > 0.5r 500 and a slope of −1.50 in between. Analysis of the substructure in the pressure and entropy maps reveals somewhat larger fluctuations around the mean pressure profile compared to the entropy. Typically, pressure fluctuations are found at the 30% level, while the entropy fluctuations are at the 20% level (rms). We compare the cumulative distribution of the substructure level in the REFLEX-DXL sample with the results of numerical simulation, and by means of KS test, show that they are in agreement. A discussion of the origin of the substructure is provided on an individual cluster basis.
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