Cosmological Constraints from the Rosat Deep Cluster Survey

The ROSAT Deep Cluster Survey (RDCS) has provided a new large deep sample of X–ray selected galaxy clusters. Observables such as the flux number counts n(S), the redshift distribution n(z) and the X-ray luminosity function (XLF) over a large redshift baseline (z∼ 0.8) are used here in order to constrain cosmological models. Our analysis is based on the Press–Schechter approach, whose reliability is tested against N–body simulations. Following a phenomenological approach, no assumption is made a priori on the relation between cluster masses and observed X–ray luminosities. As a first step, we use the local XLF from RDCS, along with the high–luminosity extension provided by the XLF from the Brightest Cluster Survey, in order to constrain the amplitude of the power spectrum, σ8, and the shape of the local luminosity–temperature, Lbol–T , relation. We obtain σ8 = (0.58± 0.06)× Ω−0.47+0.16Ω0 0 for flat models (ΩΛ = 1 − Ω0) and σ8 = (0.58 ± 0.06) × Ω−0.53+0.27Ω0 0 for open models (ΩΛ = 0) at 90% confidence level, almost independent of the Lbol–T shape. The density parameter Ω0 and the evolution of the Lbol–T relation are constrained by the RDCS XLF at z > 0 and the EMSS XLF at z̄ = 0.33, and by the RDCS n(S) and n(z) distributions. By modelling the evolution for the amplitude of the Lbol–T relation as (1+ z), an Ω0 = 1 model can be accommodated for the evolution of the XLF with 1∼ A∼ 3 at 90% confidence level, while Ω0 = 0.4 −0.2 and Ω0∼< 0.6 are implied by a non–evolving Lbol–T (A = 0) for open and flat models, respectively. Subject headings: Cosmology: theory dark matter galaxies: clusters: general X-rays: galaxies